Recommended Practices for Floating Lidar Systems

Transcription

IEA Wind Annex 32 Work Package 1.5
State-of-the-Art Report:
Recommended Practices for Floating Lidar
Systems
Issue 1.0, 2 February 2016
Oliver Bischoff & Ines Würth (University of Stuttgart)
Julia Gottschall (Fraunhofer IWES)
Brian Gribben (Frazer-Nash Consultancy)
Jonathan Hughes (The Offshore Renewable Energy Catapult)
Detlef Stein (DNV GL)
Hans Verhoef (Energy research Centre of the Netherlands (ECN))
The IEA WIND Task 32 functions within a framework created by the International Energy Agency
(IEA). Views, findings and publications of IEA WIND Task 32 do not necessarily represent the views
or policies of the IEA Secretariat or of all its individual member countries.
IEA Wind Annex 32 Work Package 1.5.
State-of-the-Art Report: Recommended Practices for Floating LIDAR Systems
Issue 1.0, 2 February 2016.
FOREWORD
The International Energy Agency Implementing Agreement for Co-operation in the Research, Development
and Deployment of Wind Energy Systems (IEA Wind) is a vehicle for member countries to exchange
information on the planning and execution of national, large-scale wind system projects and to undertake cooperative research and development projects called Tasks or Annexes.
The current document is a state-of-the-art report resulting from Task 1.5 under IEA Wind Annex 32. It
represents the authors’ collective view on currently recommended practices for the use of floating lidars for
wind resource assessment. It should be noted that work on this Task continues, and it is intended to further
develop the content of this document to the status of an IEA Wind Recommended Practices document or
other IEA Wind Executive Committee approved document as described below.
As a final result of research carried out in the IEA Wind Tasks, Recommended Practices, Best Practices, or
Expert Group Reports may be issued. These documents have been developed and reviewed by experts in
the specialized area they address. They have been reviewed and approved by participants in the research
Task, and they have been reviewed and approved by the IEA Wind Executive Committee as guidelines
useful in the development and deployment of wind energy systems. Use of these documents is completely
voluntary. However, these documents are often adopted in part or in total by other standards-making bodies.
A Recommended Practices document includes actions and procedures recommended by the experts
involved in the research project.
A Best Practices document includes suggested actions and procedures based on good industry practices
collected during the research project.
An Experts Group Studies report includes the latest background information on the topic as well as a survey
of practices, where possible.
Previously issued IEA Wind Recommended Practices, Best Practices, and Expert Group Reports can be
found at www.ieawind.org .
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PREFACE
Floating lidar systems (FLS) have emerged as wind resource assessment tools for offshore wind farms, with
the potential for greatly reduced installation costs compared to fixed met masts in some cases. The
challenges that FLS face and have to overcome to be considered as effective wind measurement options
can broadly be grouped in two categories:

The movement of the sea imparting motion on the lidar, and the subsequent challenge of
maintaining wind speed and direction accuracy;

The remoteness of the deployed system necessitating robust, autonomous and reliable operation of
measurement, power supply, data logging and communication systems.
There is no standard and few supporting documents that describe how a FLS should be deployed to get the
best quality data for a wind resource assessment. A recommended practice document is therefore required
to guide the use of FLS as a data source in wind resource assessments that lead to predictions of annual
energy production.
The goal of this document is to codify existing industry and academic best practices to help ensure that the
best quality FLS data are made available for use in the wind energy resource assessment process.
This document has been developed by a group of FLS expert practitioners and reviewed by experienced
industry stakeholders.
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CONTENTS
1.
INTRODUCTION
1.1 THE NEED FOR A RECOMMENDED PRACTICE
1.2 DOCUMENT GOAL
1.3 CALIBRATION, VERIFICATION AND VALIDATION
1.4 APPLICABILITY
1.5 LIMITATIONS
1.6 USING THIS DOCUMENT
1.7 AUTHORS
1.8 REVIEWERS
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2.
CONFIGURATION
2.1 USING THIS SECTION
2.2 OVERALL CONFIGURATION
2.3 LIDAR SYSTEM
2.4 POWER SYSTEM
2.5 DATA LOGGING AND COMMUNICATION
2.6 ANCILLARY MEASUREMENT EQUIPMENT
2.7 FLOATING PLATFORM
2.8 STATION KEEPING
2.9 TRANSPORTATION OF FLS TO SITE
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3.
CHARACTERISTATION
3.3 LIDAR SYSTEM
3.4 POWER SYSTEM
3.8 STATION-KEEPING
3.9 TRANSPORTATION OF FLS TO SITE
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4.
ASSESSMENT OF SUITABILITY
4.3 LIDAR SYSTEM
4.4 POWER SYSTEM
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4.8
4.9
MOORING
TRANSPORTATION OF FLS TO SITE
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5.
TRIAL CAMPAIGN DESIGN
5.1 OVERVIEW
5.2 PRE-DEPLOYMENT CHECKS
5.3 LOCATION
5.4 EQUIPMENT AND FACILITIES
5.5 MEASURED QUANTITIES
5.6 FUNCTIONALITY CHECKS
5.7 MONITORING DURING DEPLOYMENT
5.8 POST-DEPLOYMENT CHECKS
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6.
WIND RESOURCE ASSESSMENT CAMPAIGN DESIGN
6.1 OVERVIEW
6.2 PRE-DEPLOYMENT CHECKS
6.3 LOCATION
6.4 EQUIPMENT AND FACILITIES
6.5 MEASURED QUANTITIES
6.6 FUNCTIONALITY CHECKS
6.7 MONITORING DURING DEPLOYMENT
6.8 POST-DEPLOYMENT CHECKS
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7.
TRIALS RESULTS ASSESSMENT
7.1 INDEPENDENCE OF RESULTS ANALYSIS
7.2 WIND SPEED AND DIRECTION ACCURACY
7.3 SENSITIVITY OF WIND SPEED AND DIRECTION
ACCURACY RESULTS
7.4 AVAILABILITY
7.5 ACCEPTANCE CRITERIA
7.6 ASSESSMENT OF UNCERTAINTY OF FLS
MEASUREMENTS
7.7 LESSONS LEARNT
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WIND RESOURCE ASSESSMENT
8.1 INDEPENDENCE OF RESULTS ANALYSIS
8.2 WIND SPEED AND DIRECTION ACCURACY
8.3 SENSITIVITY OF WIND SPEED AND DIRECTION
ACCURACY RESULTS
8.4 AVAILABILITY
8.5 ACCEPTANCE CRITERIA
8.6 ASSESSMENT OF UNCERTAINTY OF FLS
MEASUREMENTS
8.7 LESSONS LEARNT
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9.
RECOMMENDATIONS FOR FURTHER WORK
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10.
BIBLIOGRAPHY
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APPENDIX: PLANNING AND PERMITTING
10.2 NOTES AND RECOMMENDATIONS RELATED TO
PERMITTING
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LIST OF FIGURES
Figure 1: Layout of this document and notional project timeline. Red, Blue and Green routes are described in
Section 1.6. ...................................................................................................................................................... 17
Figure 2: Examples of wind speed correlations from various sources. (Note that the recommended practice is
to use single-variant regression, whereas these figures also show two-variant regressions.) ....................... 50
Figure 3: Examples of wind direction correlations from various sources ........................................................ 51
Figure 4: Examples of wind speed error sensitivity to different factors from various sources ........................ 52
LIST OF TABLES
Table 1: List of reviewers ................................................................................................................................. 18
Table 2: Description of OWA Roadmap [10] maturity stages for floating lidar systems. ................................. 25
Table 3: Availability/reliability Criteria from OWA Roadmap [10]. Note that availability metric definition are
described in Section 7.4. ................................................................................................................................. 33
Table 4: Wind speed and direction accuracy criteria from OWA Roadmap [10]. Note that applicable data
ranges and availabilities are described in Section 7.2. ................................................................................... 33
Table 5: Summary of approach for wind speed and direction suitability assessment, relating to OWA
Roadmap [10] assessment criteria. ................................................................................................................. 33
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LIST OF RECOMMENDED PRACTICES
RP 1: Essential Components.
RP 2: Metocean Sensors.
RP 3: Modular Construction.
RP 4: System Redundancy.
RP 5: Model of lidar is accepted in the industry.
RP 6: Power sources.
RP 7: Data logging system.
RP 8: Communications system – real time.
RP 9: Communications system – redundancy.
RP 10: Communications system – wireless.
RP 11: Metocean sensors.
RP 12: Secondary wind speed and direction sensors.
RP 13: Safe access to the FLS for personnel.
RP 14: Access from work boats.
RP 15: Navigation aids.
RP 16: Watch circle monitoring.
RP 17: Design of mooring system.
RP 18: Transportation of the FLS.
RP 19: Towing bridle.
RP 20: Summary of system characteristics.
RP 21: Supplier assessment of FLS maturity.
RP 22: Supplier evidence of FLS maturity.
RP 23: Provision of Dimensions and Weight Information.
RP 24: Provision of operating/survivability conditions information.
RP 25: Provision of availability and maintenance information.
RP 26: Provision of Method Statement (MS).
RP 27: Lidar characterisation.
RP 28: Lidar type validation information.
RP 29: Information on use of the lidar type in the wind industry.
RP 30: Motion compensation characterisation.
RP 31: MS for lidar set-up.
RP 32: Provision of power systems information.
RP 33: Provision of data logging and communication information.
RP 34: Ancillary measurement equipment characterisation.
RP 35: MS for ancillary measurement equipment set-up.
RP 36: Maintenance access documentation.
RP 37: Examples of suitable work boats.
RP 38: Assessment of damage risk.
RP 39: Specification of navigation lights.
RP 40: Specification of geo-location system.
RP 41: Provision of station-keeping design information.
RP 42: Experience with the station-keeping system.
RP 43: MS for mooring.
RP 44: MS for dynamic station-keeping system.
RP 45: MS for transportation.
RP 46: Appropriate FLS maturity.
RP 47: Evidence of FLS maturity – wind speed and direction accuracy.
RP 48: Evidence of FLS maturity – reliability.
RP 49: Suitability of FLS Dimensions and Weight.
RP 50: Suitability of operating conditions.
RP 51: Suitability of maintenance information and regime.
RP 52: Suitability of Method Statement (MS).
RP 53: Protection from damage due to relative motion – power system.
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RP 54: Overall system evaluation – general.
RP 55: Evaluating accuracy of the lidar type.
RP 56: Wind industry acceptance of the lidar type.
RP 57: Evaluation of motion compensation – FLS trial.
RP 58: Evaluation of motion compensation – WRA deployment.
RP 59: Power storage requirement.
RP 60: Power system maintenance/replenishment requirement.
RP 61: Power system full recharge requirement.
RP 62: Evaluating data logging capacity.
RP 63: Evaluating communication system redundancy.
RP 64: Evaluating communication system – wireless system.
RP 65: Evaluating metocean sensor set-up.
RP 66: Evaluating secondary wind speed and direction sensors.
RP 67: Evaluation of the floating platform – safety systems
RP 68: Evaluation of mooring arrangement suitability for site.
RP 69: Evaluation of MS for mooring inspection.
RP 70: De-risking shock damage to the lidar
RP 71: ‘Blind’ trial principle.
RP 72: Feedback on performance
RP 73: Pre-deployment verification check on lidar unit.
RP 74: Ideal location for a FLS trial
RP 75: Specification of the reference system.
RP 76: Separation distance between FLS and reference system.
RP 77: Positioning to ensure undisturbed flow.
RP 78: Metocean measurement system.
RP 79: Ancillary measurement system.
RP 80: Synchronisation of data loggers.
RP 81: Measured Quantities - Datum.
RP 82: Measured Quantities - Comparison.
RP 83: Measured Quantities - Sensitivity.
RP 84: Recommended measurement heights for wind speed and direction in a trial.
RP 85: Recommended trial duration.
RP 86: Recommended monitoring during trial.
RP 88: Requirement for and duration of pre-deployment verification check on FLS unit.
RP 89: Post-deployment checks – lidar unit
RP 90: Independence of trial results
RP 91: Wind speed and direction correlations
RP 92: Data coverage requirements for wind speed and direction correlations
RP 93: KPIs for wind speed and direction accuracy
RP 94: Sensitivity of wind speed and direction error
RP 95: System and data availability definitions
RP 96: Other KPIs relating to availability and reliability
RP 97: FLS trial results acceptance criteria – accuracy
RP 98: FLS trial results acceptance criteria - availability
RP 99: Assessment of uncertainty resulting from performance verification test (from FLS trial results).
RP 100: Capturing and disseminating lessons learnt.
RP 101: Independence of pre-deployment checks and results analysis
RP 102: Wind speed and direction correlations: pre-deployment check
RP 103: Data coverage requirements for wind data correlations: pre-deployment check
RP 104: KPIs for wind speed and direction accuracy: pre-deployment check
RP 105: Wind speed and direction functionality checks at wind resource assessment site
RP 106: Sensitivity of wind speed and direction error: pre-deployment checks
RP 107: Wind speed and direction and sensitivity to environmental parameters
RP 110: Pre-deployment verification acceptance criteria – accuracy
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RP 111: Pre-deployment verification and wind resource assessment acceptance criteria - availability
RP 113: Engagement with authorities.
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LIST OF NOTES
Note 1: General standard of lidar. ................................................................................................................... 20
Note 2: Presence of motion compensation...................................................................................................... 20
Note 3: Considerations for power sources. ..................................................................................................... 20
Note 4: Design of the energy generation and storage system. ....................................................................... 21
Note 5: Other data sensors. ............................................................................................................................ 21
Note 6 : Emergency assistance for injured personnel ..................................................................................... 22
Note 7: Risks of damage to the FLS. ............................................................................................................... 22
Note 8: Risk of mooring failure. ....................................................................................................................... 23
Note 9 : Competency Assessment of Maintenance Staff ................................................................................ 26
Note 10: Motion compensation and degrees of freedom. ............................................................................... 27
Note 11: Accuracy and availability metrics with respect to FLS maturity claims ............................................. 32
Note 12: Deploying a FLS at a lower maturity level ........................................................................................ 34
Note 13: Oversizing components and reducndancy ........................................................................................ 35
Note 14: Evaluation of motion compensation – general. ................................................................................. 36
Note 15: Safe access to power system components. ..................................................................................... 37
Note 16: Evaluation of inclinometers and other motion sensors – general. .................................................... 38
Note 17: Ideal location for a FLS trial .............................................................................................................. 41
Note 18: Reference system for wind speed and direction. .............................................................................. 41
Note 19: Measurement heights for wind speed and direction in a trial. .......................................................... 44
Note 20: Functionality checks at the outset of a trial ....................................................................................... 45
Note 21: Regular monitoring during trial. ......................................................................................................... 45
Note 22: Post-deployment checks. .................................................................................................................. 45
Note 23: Ideal location for FLS pre-deployment check (prior to WRA deployment)........................................ 47
Note 24: Post-deployment checks – FLS unit ................................................................................................. 48
Note 25: Considerations on the FLS measurement uncertainty budget ......................................................... 54
Note 26: Assessment of uncertainty due to system classification (from FLS trial results). ............................. 54
Note 27: Considerations on the FLS measurement uncertainty...................................................................... 57
Note 28: Licensing – general. .......................................................................................................................... 61
Note 29: Licensing – vessel classification. ...................................................................................................... 61
Note 30: Specific learning points from a UK waters deployment in the Irish Sea ........................................... 61
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NOMENCLATURE
Abbreviations
AIS
Automatic Identification System, a radio-based marine vessel identification system
CNR
Carrier-to-Noise Ratio
FLS
Floating lidar system, or floating lidar systems
GPS
Global Positioning System
KPI
Key Performance Indicator
Lidar
LIght Detection and Ranging, also ‘lidar’
Met mast
Meteorological mast, or tower
MS
Method Statement
OEM
Original Equipment Manufacturer (in this context of the FLS)
RACON
A radar transponder (from RADar and beaCON) used to mark maritime navigational hazards
RSD
Remote Sensing Device, here meaning Lidar and/or Sodar
Sodar
SOnic Detection and Ranging, or SOund Detection and Ranging, also ‘SODAR’
WRA
Wind Resource Assessment
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INTRODUCTION
1.
Wind resource assessment is a maturing discipline, important to investment decisions in wind farm
development, which uses a range of information sources. Traditionally, for both onshore and offshore wind
farms, sensors mounted on meteorological masts (“met masts”) have been regarded as the ideal information
source, and often used to characterise local wind regimes in advance of constructing large wind farms.
At the time of writing (2014/15), there is no formal wind resource assessment standard. Instead, processes
for measuring the wind speed and direction and subsequent performance of a wind turbine at that site are
largely based on the International Electrotechnical Commission (IEC) 61400 family of standards [1,2]. These
standards require that wind speed measurements be made using calibrated mechanical cup anemometers
that have a documented response to changes in environmental conditions. The standards also require that
wind direction measurements be made using wind vanes. The use and deployment of cup anemometers and
vanes is backed up by calibrations (e.g. MEASNET [3]), an extensive and well-developed body of knowledge
about how they perform under different environmental conditions, well-established standards for use, and an
experienced user-community.
Non-traditional remote sensing measurement devices are being increasingly used in wind resource
assessment. The two types of device in most common use are lidar (also ‘lidar’, from LIght Detection And
Ranging) and sodar (also ‘SODAR’, from SOnic Detection And Ranging, or SOund Detection And Ranging).
They can characterize the wind resource at multiple heights from near ground to above typical wind turbine
hub heights. The deployment of remote sensing may provide wind project developers with useful information
that can be used to reduce the costs associated with wind data collection at heights greater than can be
achieved using traditional monitoring towers. The use of remote sensing as part of a well-planned and
properly implemented wind resource measurement campaign involving a diverse suite of measurement
techniques may also contribute to the overall reduction of uncertainty in a formal wind energy production
assessment. Unsurprisingly, as there is no general formal wind resource assessment standard, there is no
formal standard for the use of lidar and sodar in that context either. However, an IEA Wind recommended
practice [5] has been developed which represents a significant milestone on the route towards a standard for
this technology.
1.1
THE NEED FOR A RECOMMENDED PRACTICE
Floating lidar systems (FLS) have emerged as wind resource assessment tools for offshore wind farms, with
the potential for greatly reduced installation costs and timescales compared to fixed met masts in many
cases. The technology is not yet fully mature and there are a number of systems and concepts; at the time of
writing (2015) a small number of systems have been deployed on “real” wind resource assessments, a
greater number have recently undergone, are currently undergoing, or are planned to undergo sea trials, and
still further systems are under development. Despite all these activities, compared to the use of cups and
vanes for wind resource assessment, or even compared to the use of lidars for onshore projects, the level of
usage and associated expertise is currently still small. The challenges that FLS face and have to overcome
to be considered as effective wind measurement options can broadly be grouped in two categories:

The movement of the sea imparting motion on the lidar, and the subsequent challenge of
maintaining wind speed and direction accuracy;

The remoteness of the deployed system necessitating robust, autonomous and reliable operation of
measurement, power supply, data logging and communication systems.
There is no standard and few supporting documents that describe how a FLS should be deployed to get the
best quality data for a wind resource assessment. A recommended practice document is therefore required
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to guide the use of FLS as a data source in wind resource assessments that lead to predictions of annual
energy production.
This document is described as recommended practice rather than best practice for three reasons. Firstly, to
the authors’ knowledge this is the industry’s first attempt to collectively gather good practice, and therefore to
assert that this is best practice seems premature. Second, the track record of FLS deployments is relatively
short, so the evidence base for asserting “best” as opposed to “currently recommended” practice does not
exist yet. Third, this document is more authoritative and comprehensive in some areas than in others, so is
not thought to be complete enough (yet) to qualify as best practice. This last point is expanded on in Section
1.6.
1.2
DOCUMENT GOAL
The goal of this document is to combine and codify existing industry and academic good practices, and
elements of related standards and guidelines, to help ensure that the best quality FLS data are made
available for use in the wind energy resource assessment process. This includes practices to reduce the
uncertainty of data and practices promoting high data availability during a measurement campaign.
1.3
CALIBRATION, VERIFICATION AND VALIDATION
It is useful to introduce some definitions of commonly used words for which meaning often overlaps in
common usage:

Calibration: operation that, under specified conditions, in a first step, establishes a relation between
the quantity values with measurement uncertainties provided by measurement standards and
corresponding indications with associated measurement uncertainties and, in a second step, uses
this information to establish a relation for obtaining a measurement result from an indication

Verification: provision of objective evidence that a given item fulfils specified requirements

Validation: verification, where the specified requirements are adequate for an intended use.
These definitions come from the International Vocabulary of Metrology [4]. To provide some context, in the
IEA Wind recommended practice for the use of remote sensing devices [5], verification is widely used for
the act of comparing RSD measurements against those from cup anemometers, and calibration is used for
example as the act of relating a cup anemometer’s rotational speed to a measurement standard wind speed
in a wind tunnel. As such these uses are consistent with the above definitions. It is noted also that although
the use of the word validation is absent from [5], verification is always carried out with the purpose of
validating the device for a specific use, therefore the terms are very similar in meaning in this context.
For the current purpose concerning FLS, we will prefer the term validation as the act of obtaining
confidence in a system’s measurement accuracy, by comparing with measurement results from other
systems with established accuracy, which will be, or will be derived from, a calibrated measurement device.
1.4
APPLICABILITY
This document is designed to guide the use of lidars mounted on floating platforms for the resource
assessment phase of an offshore wind farm development, or for trials of such systems intended for that
application. In this context, the lidar is assumed to be of the types currently in most common use for this
purpose, i.e. of fixed scan geometry and vertically-profiling. As well as a location to site the lidar, the floating
platform is assumed to house or mount associated systems suitable for autonomous operation, namely
power and communication systems. The floating platform itself is assumed to consist of a tethered buoy,
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which is inclusive of both quasi-static (“spar buoy”) and more standard marine buoys which float on the
surface and move substantially with waves (here called a “marine buoy”).
The lidar types assumed here are consistent with the lidar types considered in the Remote Sensing Device
(RSD) recommended practice [5], namely lidars which measure a vertical profile, and excludes those
measuring in a horizontal manner. Furthermore, in this document it is assumed that the FLS supplier
provides mean wind speed and direction data for a specific height over a period of time, which is assumed to
be a 10 minute period. The derivation of time-averaged quantities from instantaneous quantities by the end
user is not recommended. To relate this document to that for (RSD) recommended practice [5], here the
focus is on using Time-averaged wind vector data (section 5.1.3 of [5]) rather than Instantaneous wind vector
data (section 5.1.2 of [5]).
Use of FLS for other purposes (for example wake effects or power curve studies) is not directly addressed by
this document, however some of the practices presented here may be helpful in guiding such deployments.
As stated above, guiding the use of FLS for wind resource assessment (or trialling of a FLS with that
purpose in mind) is the overall purpose of this document. In so doing, all of this document will be of interest
to the Original Equipment Manufacturers (OEMs) of FLS. In particular, new entrants to the OEM market will
find configuration advice on the make-up of a FLS in Section 2, and OEMs at the point of supplying their
systems or services will find advice on how to characterise their FLS in Section 3.
1.5
LIMITATIONS
The recommended practices in this document are intended to complement training and documentation
provided by FLS manufacturers or suppliers. This document has been written assuming that the reader is
familiar with the basic process of wind resource assessment and typical wind instrumentation, and is not
intended to be a ‘how-to’ guide for the process of wind resource assessment. This document does not
provide information on when to use a FLS in preference to or in combination with other measurement
systems.
Use of FLS for the measurement of wind speed and direction is within scope; as their use for other purposes
including measurement of turbulence and gusts is at a far lower level of maturity this is not within scope.
(However, some related notes and advice do appear in this document as it is prudent to manage such
measurements well, even if we have to wait for understanding to develop on how to confidently exploit the
data.)
The recommended practices are not provided as a complete set of all practices to be adopted to ensure a
successful wind measurement campaign using FLS; rather, they are a collection of individual recommended
practices which have emerged from the expert and user community whose adoption will benefit the industry
as a whole and provide a useful benchmark.
Most importantly, in areas where there are safety implications, for example (but not limited to) system
deployment and mooring, observations and recommendations are made here from the wind resource
assessment point of view, and these are not commensurate to safety guidelines.
1.6
USING THIS DOCUMENT
This document is structured such that the subject matter is presented in an order notionally consistent with a
project timeline for a FLS deployment. This order and the main section headings are summarised in Figure
1. An overview of each of these sections is described below:
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
Configuration. There is sufficient industry experience to inform requirements on the make-up of the
FLS, for example which components should be present and what their specifications should be;
these are detailed in this section.

Characterisation. There are a number of different FLS models available from different suppliers,
and each model has its own characteristics. These characteristics should be detailed by the FLS
original equipment manufacturer (OEM) so that the procurer of an FLS or of FLS services has a
good understanding of what they are procuring. Also, in the event of problems arising during
deployment there is a desire to understand the issues and determine a remedial plan of action, and
experience has shown that having a written system description at an appropriate level of detail can
be of real benefit. This section details the information which should be supplied by the OEM in order
to characterise the system to an adequate level. This characterisation is in broad terms a detailing of
the elements of the Configuration section, and the data provided is an important part of Assessment
of Suitability.

Assessment of Suitability. This section describes recommended practices for determining whether
a candidate FLS is suitable for deployment in an offshore FLS trial or for WRA purposes. This
consists of evaluating the information provided by the OEM (Characterisation), and refers to the
OWA Roadmap [10].

Trial Campaign Design. This section describes recommended campaign parameters for the case
where the purpose of the deployment is to trial a FLS, and refers to the OWA Roadmap [10].
Specification for recommended reference measurement systems is included in this section.

Wind Resource Assessment Campaign Design. This section describes recommended campaign
parameters for the case where the purpose of the deployment is to support wind resource
assessment.

Trials Results Assessment. If the purpose of the deployment is to trial a FLS, the question arises
as to how to best assess the results of that trial. This section describes the required data processing
and comparisons and also relevant compliance and acceptance thresholds. This section also refers
to the OWA Roadmap [10].

Wind Resource Assessment. Recommended practice in processing and accepting the measured
data in support of wind resource assessment is described here.

Planning and Permitting. This section sits outside the main flow of the document, and collects
experiences in obtaining the necessary planning consent, permits and/or licenses for the deployment
of a FLS.
As indicated on Figure 1, three different reader objectives, and routes to those objectives, are considered:

Planning and performing a FLS Trial – Red Route.

Planning and performing a wind resource assessment campaign using a FLS, where trialling the FLS
has not yet been performed and is part of the planned campaign – Green Route.

Planning and performing a wind resource assessment campaign using a FLS, where a FLS trial has
already been successfully performed – Blue Route.
It is recognised that this collection is more comprehensive and therefore authoritative in certain sections than
in others. Items relating to mooring, installation, licensing, and safety are in particular advisory in nature and
fall well short of being comprehensive. For this reason these topics feature in the Recommendations for
Future Work section, along with a collection of other points.
16
This document highlights two different results in the text with an underlined, bold label and number. For
example:

Note 1. These points are for information only and may explain or expand on a recommended
practice. They may also highlight where more research or development is required.

RP 1. These points are the specific recommended practices that should be followed.
2. CONFIGURATION
3. CHARACTERISATION
Appendix:
PLANNING &
PERMITTING
4. ASSESSMENT OF
SYSTEM SUITABILITY
5. TRIAL CAMPAIGN
DESIGN
7. TRIAL RESULTS
ASSESSMENT
6. WIND RESOURCE
ASSESSMENT
CAMPAIGN DESIGN
8. WIND RESOURCE
ASSESSMENT
PROJECT
TIMELINE
Figure 1: Layout of this document and notional project timeline. Red, Blue and Green routes are
described in Section 1.6.
17
1.7
AUTHORS
This document was drafted by:

Oliver Bischoff (University of Stuttgart)

Julia Gottschall (Fraunhofer IWES)

Brian Gribben (Frazer-Nash Consultancy)

Jonathan Hughes (The Offshore Renewable Energy Catapult)

Detlef Stein (DNV GL)

Hans Verhoef (Energy research Centre of the Netherlands (ECN))

Ines Würth (University of Stuttgart)
The authors of the current document are also indebted to the authors of the fore-running IEA Wind document
on RSD recommended practice [5], which can be seen as the starting point for the present work and from
which much of the layout and style and indeed some of the introductory material has been borrowed. This
recommended practice builds on information that is publicly available, including results from floating lidar
trials reported in peer-reviewed journal and conference papers [6,7,8,9] and the Offshore Wind Accelerator
commercialisation roadmap [10]. All sources are cited in the text and a complete list of references is given in
the Bibliography (Section 10). The reader is recommended to consult documentation provided by the FLS
suppliers in addition to these materials.
1.8
REVIEWERS
This document has been reviewed by subject matter experts in national laboratories, academia, and the wind
energy industry. These reviewers are identified (in no particular order) in Table 1. All comments and
contributions were helpful and appreciated.
Country
Belgium
Canada
Denmark
France
Germany
Japan
Norway
Spain
UK
UK
UK
UK
USA
Organisation
FLIDAR
AXYS Technologies
DONG Energy
Leosphere
DEWI
Mitsubishi Electric
Fugro
IREC
RWE
Zephir
SeaRoc
Babcock Marine & Technology
NREL
Table 1: List of reviewers
18
Name
Matthias Borremans
Graham Howe
Nicolai Gayle Nygaard
Matthieu Boquet, David Langohr
Beatriz Canadillas
Shumpei Kameyama
Arve Berg
Miguel Angel Gutierrez
John Slater
Mark Pitter
Jane Haviland
Andy Paterson
Andy Clifton
CONFIGURATION
2.
There is sufficient industry experience to inform requirements on the make-up of the FLS, for example which
components should be present and what their specifications should be; these are detailed in this section.
This section is closely related to Section 3 and Section 4, where characterisation and suitability assessment
recommended practices are described.
2.1
USING THIS SECTION
For those planning to use a FLS for wind resource assessment, or planning to trial a FLS for that purpose,
this section is useful for:

Providing a general background on the recommended make-up of FLS systems;

Providing a means to perform an initial assessment of the suitability of a candidate FLS system.
This section should also be useful for FLS OEMs or potential FLS OEMs, particularly those considering
entering the supplier market, as it provides a general perspective on the requirements of the system makeup.
Note that the related topic of the detailed information which it is recommended that the FLS supplier provides
is described in Section 3. Also, recommendations on how to make a detailed assessment of FLS capability is
described in Section 4.
2.2
OVERALL CONFIGURATION
RP 1: Essential Components.
The FLS should consist of the following essential components:

Lidar;

FLS operating system;

Power system;

Data logging and communication;

Floating platform;

Safety system;

Station-keeping system.
The supplier of the FLS should supply all components as an integrated system; integration of individual
components by the owner / customer is not recommended.
All components should be suitable for use in a marine environment and have certification and/or warranties
that meet the planned campaign duration.
RP 2: Metocean Sensors.
The FLS should also feature metocean sensors (to measure wave height and wave period), or alternatively
be deployed in conjunction with separate metocean sensors. (The specific metocean characteristics which
should be available are those also specified in Section 5.5.)
19
RP 3: Modular Construction.
It is advisable to modularise the construction to allow offshore replacement rather than full recovery of the
FLS. This applies to the lidar unit, batteries, renewable power generation units, communication components
and data logger as a minimum.
RP 4: System Redundancy.
It is advisable to consider system redundancy in the overall scheme design, for example in the mooring
system, the power generation and storage system, data storage and communications systems.
2.3
LIDAR SYSTEM
Note 1: General standard of lidar.
The capability of the type of lidar unit being employed should meet current industry expectations in onshore
and/or offshore fixed platform configurations. A batch-produced model which has demonstrated its suitability
for use in a marine environment will inevitably be considered less risky than a one-off prototype system.
RP 5: Model of lidar is accepted in the industry.
The model of lidar on the FLS should have a history of successful use in wind resource assessments. Massproduced systems that have a stable engineering design are recommended over prototype systems.
Note 2: Presence of motion compensation.
The FLS may or may not include motion compensation systems. In either case evidence should be provided
which justifies the design (see Sections 4.2 and 4.3).
2.4
POWER SYSTEM
RP 6: Power sources.
All FLS should include an intelligent power system that prioritizes safe operation of the FLS. For example,
navigation lights should have priority over other systems in low-energy situations.
Note 3: Considerations for power sources.
The power requirements of the FLS could be met by a number of power sources. The most commonly used
power sources are a combination of renewable (solar and wind) devices used in conjunction with
rechargeable batteries and/or fuel cells. Liquid-fuelled generators are also used in some systems.
Performance of onboard wind turbines can be less than anticipated, probably due to aerodynamic
interference from the structure itself.
Independent solar-powered navigation lights are available as primary or backup lights. These can provide
some redundancy in the FLS lighting in the event of catastrophic power system failure.
Solar panels may be susceptible to impact damage if not adequately protected for the installation and
storage methods chosen.
Bird fouling and marine growth (e.g. algae) has been known to seriously degrade solar panel performance.
The circumstances in which this can happen, and design measures to prevent or mitigate this effect, do not
appear to be well understood in the industry.
An under-estimation of power requirements, and over-estimation of renewable power source effectiveness,
are known causes of availability problems.
20
The relative motion between the floating platform and a stabilised lidar device can cause wear and damage
to cables.
Note 4: Design of the energy generation and storage system.
There are multiple approaches to ensuring that adequate power is available to the FLS at all times. Different
combinations of generation and storage capacity, redundancy, and robustness may all result in a satisfactory
system. The ease or difficulty of swapping out components, and distance from port, may also be factors. For
these reasons no specific combination is recommended.
2.5
DATA LOGGING AND COMMUNICATION
RP 7: Data logging system.
The data logging system should have on-board storage capacity sufficient for the planned duration of the
deployment, with an extra 3 months worth of storage for contingency.
RP 8: Communications system – real time.
The communications system should enable data transfer to shore in real time, or close to real time. If power
or bandwidth is limited, a subset of diagnostic data that includes system performance and health should be
defined and take precedence over other data.
RP 9: Communications system – redundancy.
The communications system should have more than one channel of communication (e.g. cell phone network
protocols, satellite communications, radio). Switching between channels of communication should be
automatic or under remote control.
RP 10: Communications system – wireless.
The communications system should include a wireless communication channel suitable for use from a
nearby work boat.
2.6
ANCILLARY MEASUREMENT EQUIPMENT
RP 11: Metocean sensors.
It is essential that, while the lidar unit is recording wind speed and direction, the sea state is also
simultaneously measured, and those sea state data are recorded. This could be achieved through sensors
mounted on the floating platform, or through other sensors deployed separately in the vicinity. Metocean
sensors should be designed for marine conditions. Metocean sensors should have a history of successful
use in meteorological and oceanographic applications. Mass-produced systems that have a stable
engineering design are recommended over prototype systems. (Details of the metocean measurements
required are included in Section 5.5.)
RP 12: Secondary wind speed and direction sensors.
It is essential that, while the lidar unit is recording wind speed and direction, secondary sensors are
recording the same quantities for use as a cross-check to verify operation. Cup anemometers and wind
vanes, sonic anemometers, or standing-wave anemometers deployed 1 to 2 m above platform level are
sufficient for this application.
Note 5: Other data sensors.
In addition to the lidar and metocean sensors, it is recommended to have additional sensors on the FLS to
provide cross checks on the primary sensors, to provide additional wind resource data, to understand the
21
lidar performance, and to provide a broader dataset to support future data analysis. Examples of additional
data that may be required include:

Air temperature;

Humidity;

Air pressure;

Vertical air temperature profiling – acknowledging that this is currently difficult to achieve;

Buoy motion;

Video (e.g. to monitor bird fouling, or remote from the FLS to monitor overall status).
With respect to FLS trials, where FLS wind measurements are compared with those from reference systems,
specification for recommended reference measurement systems is included in Section 5.
2.7
FLOATING PLATFORM
RP 13: Safe access to the FLS for personnel.
In the case where maintenance access onto the buoy for personnel is required, the floating platform should
have provision for safe boarding, including access points and space for at least two people to board the
platform and access all systems. Safety features such as handrails, attachment points, and fenders should
be part of the design.
It must be possible to verify before boarding that the FLS buoy is de-energized. This reduces the risk of
electric shock due to shorts to the buoy hull and other faults.
RP 14: Access from work boats.
The floating platform should be accessible from a variety of work boat sizes and types (which should be
specified by the supplier, see Section 3.7).
Note 6 : Emergency assistance for injured personnel
It is noted that should a person become unconscious, or unable to disembark the FLS unaided, it may be
required to have 3 people on the FLS (the injured party and 2 others acting as rescuers). The design
assessment should take this into account. Consideration should also be given to rescue of casualties and
transfer back to a work boat of stretcher bound and/or unconscious casualties.
Note 7: Risks of damage to the FLS.
FLS systems have been damaged by sea mammals and subject to vandalism. The risk of damage due to
these causes is very dependent on location. The design should be resistant to tampering and damage, and
utilize tamperproof screws, locked hull compartments and dry boxes, and underwater or out-of-reach sensor
mounts.
RP 15: Navigation aids.
All buoys should have aids to navigation that conform to local requirements. These may be specified by the
Coastguard or local equivalent. Also consider use of radio or radar-based identification systems such as AIS
and RACON.
RP 16: Watch circle monitoring.
The FLS should monitor its location within a specified watch circle using GPS or equivalent. If the FLS
moves outside this watch circle, an emergency notification should be sent to shore via communication
22
channels. This message should include the location of the buoy. This information is required to warn
shipping and aid in recovery.
2.8
STATION KEEPING
Station keeping can be achieved through active or passive means. Active station keeping can be achieved
through dynamic positioning using motors. Passive station keeping is more common, and typically takes the
form of a mooring (anchor plus mooring line). Buoy motion in either case is restricted to an area known as
the watch circle.
Note 8: Risk of mooring failure.
There are known instances of mooring or tethering failure, with resulting loss or significant damage to the
FLS, notwithstanding risk to shipping. Such failures are seen as a major risk factor for FLS deployment.
RP 17: Design of mooring system.
This RP applies only to station-keeping systems of the mooring type. Mooring designs are site specific. A
mooring design is not necessarily transferable from one site to another. Moorings must be designed
according to local conditions and regulations by qualified experts. Only use components from reputable
suppliers. A third-party review of the mooring design is recommended.
2.9
RP 18: Transportation of the FLS.
It is recommended to transport the FLS from the quayside to site complete and commissioned to reduce
quayside cost, time and complexity.
RP 19: Towing bridle.
If the FLS is to be towed, reducing the length of towing bridle where possible and minimising opportunities
for snagging are desirable to prevent mishaps in deployment and retrieval.
23
CHARACTERISTATION
3.
There are a number of different FLS models available from different suppliers, and each model has its own
characteristics. These characteristics should be detailed by the FLS original equipment manufacturer (OEM)
so that the procurer of an FLS or of FLS services has a good understanding of what they are procuring. Also,
in the event of problems arising during deployment there is a desire to understand the issues and determine
a remedial plan of action, and experience has shown that having a written system description at an
appropriate level of detail can be of real benefit. This section details the information that should be supplied
by the OEM in order to characterise the system to an adequate level, which is known as the FLS data pack.
The Configuration section (Section 2) provides recommendations on how a FLS should be configured; this
section provides recommendations on what information should be supplied to understand how a specific FLS
system is configured; and the data provided is an important part of the Assessment of Suitability (Section 4)
of the specific FLS system.
3.1
USING THIS SECTION
this section is useful for:

Assessing whether the detailed information supplied by the FLS service provider is sufficient to
assess suitability;

Ensuring that sufficient FLS information is gathered such that the procurer of FLS services is in an
informed position should operational problems arise.
This section should also be useful for FLS OEMs, as it provides guidance on the nature of the system
information which the FLS user will expect and/or require.
Note that the related topic of recommendations on how to make a detailed assessment of FLS capability is
described in Section 4.
3.2
RP 20: Summary of system characteristics.
An overall description of the system should be delivered by the supplier. This data pack should include at
least:

The lidar type and model;

Whether the buoy is of spar-buoy or marine buoy type;

Whether motion compensation is employed: if so, what degrees of freedom are compensated, and
whether this is applied in hardware and/or software;

The metocean and/or other sensors included in the FLS;

The on-board power sources;

The communication channels;

A schematic diagram of the FLS.
24
RP 21: Supplier assessment of FLS maturity.
The supplier should specificy the level of system maturity that is claimed for the overall FLS, according to the
maturity categories defined in the OWA Roadmap [10] and summarised in Table 2.
RP 22: Supplier evidence of FLS maturity.
The supplier should supply independently verified evidence to support their assessment of the FLS maturity
level. This evidence should include information about wind speed and direction accuracy and system
reliability.
Stage
1.
Baseline
2.
Pre-Commercial
3.
Commercial
Description
As a pre-requisite, the lidar measurement unit itself should have
achieved wide-spread acceptance within the onshore wind industry as
"proven" in the field of wind resource characterisation for non-complex
terrain sites at least.
Following a successful pilot validation trial, the floating lidar technology
may be utilised commercially in limited circumstances - specifically in
conditions similar to those experienced during the trial. Elevated
measurement uncertainty assumptions may be expected for such
application, when benchmarked against the deployment of a
conventional fixed offshore meteorological mast.
Following successful further trials and early commercial deployments
covering a range of site conditions, a sufficient body of evidence is
accumulated to relax the elevated uncertainty assumptions.
Table 2: Description of OWA Roadmap [10] maturity stages for floating lidar systems.
RP 23: Provision of Dimensions and Weight Information.
The data pack provided by the FLS supplier should include detailed drawings and text that include:

The overall dimensions of the FLS when out of the water.

The submerged depth and protruding height (including ranges if applicable) of the deployed FLS.

The overall weight of the FLS.

Dimensions applicable to the approach of, and access of personnel from, maintenance vessels, e.g.
touchpoints, overhangs, depths, and maximum and minimum heights of vessel fenders.

The watch circle of the deployed FLS.
RP 24: Provision of operating/survivability conditions information.
The data pack provided by the FLS supplier should include:

The design operating temperature range.

The design operating ranges of metocean conditions (see Section 5.5).

The design operating range of wind speed.

The design operating range of water depth.

Consequences, including data loss, data accuracy, and system integrity, if these ranges are exceeded.
25
The data pack should also include information on the range of conditions (beyond the operating range) in
which the FLS is expected to survive.
RP 25: Provision of availability and maintenance information.

The nominal system availability when deployed.

The nominal longevity of a deployment without maintenance visits.

The offshore maintenance regime, including details of consumables and their replenishment schedule.

The nominal longevity of a deployment before recovery and onshore maintenance is required.

The service interval for the lidar system and whether this can be performed offshore or by returning to
base for factory conditions servicing. Also whether the lidar can be safely removed and/or replaced at
sea or whether a harbour visit is recommended.

Advice on proper storage conditions.

Information on any required scheduled maintenance including maintenance schedule, even if the FLS
is not being used.
Note 9 : Competency Assessment of Maintenance Staff
It should be noted that the offshore training requirements for FLS maintenance staff can vary and additional
training may need to be scheduled to satisfy differing national/company requirements.
RP 26: Provision of Method Statement (MS).
The data pack provided by the FLS supplier should include a Method Statement (MS) for the deployment
and recovery of the FLS. Where applicable, the MS should also include a description of how major
components (lidar unit, batteries, renewable power generation units, communication components and data
logger as a minimum) can be replaced in situ during an offshore deployment.
3.3
LIDAR SYSTEM
RP 27: Lidar characterisation.
The data pack provided by the FLS supplier should include a full description of the lidar employed, and the
associated wind speed and direction measurement. This description should include:

Lidar-related characterisation, as detailed in RP1 of [5] and not reproduced here.

A detailed description of how the wind direction (in a global reference frame) is to be determined,
noting that the orientation of the lidar may vary.

A description of how the wind speed is determined, namely whether it comes directly from the lidar
as for a static deployment, or whether there are hardware and/or software motion compensation, and
whether any software compensation is applied automatically or as a post-processing step. Note that
“Motion Compensation” details are required, see below.

If any other quantities are measured by the lidar, for example turbulence or gust speeds, these
should also be specified, the manner in which they are determined explained, and any required postprocessing specified.
26

A detailed description of the data file that is provided to the users which records the measured data
by the lidar. (Note that if the FLS uses any form of motion compensation, then the provided data file
may differ from that provided by the lidar unit in isolation, but the same requirement to describe the
data file applies).

A detailed description of any applicable or variable filters on data quality, noting that these may be
applied automatically by the system, may be applied as a post-processing step by the supplier, or
may even be applied by the user as a post-processing step. A common such filter is for Carrier to
Noise Ratio (CNR); for example the FLS supplier may detail which CNR threshold is applied
automatically, or alternatively for example recommend an applicable CNR threshold and describe
how a threshold can be applied to the data file.
RP 28: Lidar type validation information.
The data pack provided by the FLS supplier should include evidence of the testing that the lidar has
undergone at suitable test sites. This information may be used to substantiate the lidar maturity level and
lidar performance claims.
RP 29: Information on use of the lidar type in the wind industry.
The supplier should report the extent to which the lidar has been used in WRA campaigns.
Note 10: Motion compensation and degrees of freedom.
The motion of the buoy can be described as six degrees of freedom (DOF). The six DOF include translation
along and rotation about three axes: vertical axis, longitudinal axis and lateral axis. For translation motion,
these are often referred to as heave, surge and sway respectively. Likewise for rotational motion, these are
often referred to as yaw, roll and pitch respectively. Where motion compensation is present, it is most often
applied to pitch and roll, however in principle motion compensation can be applied to any (or none) of these
degrees of freedom.
RP 30: Motion compensation characterisation.
The data pack provided by the FLS supplier should include a description of motion compensation systems
and related design features, including:

Maximum angle from the vertical from which the lidar’s vertical axis will deviate during operation and
the frequency of this occurrence..

Maximum angular velocity that the lidar’s vertical axis will experience in operation.

Maximum horizontal and vertical components of velocity (in a global frame of reference) that the lidar
will experience in operation.

Specification of any motion compensation arrangements, which can consist of more than one of the
following:
o
Passive/Mechanical. Unpowered, mechanical arrangements whereby the motion of the lidar
due to the motion of the floating platform is reduced or negated. This could include gimbal or
spring mounting, in which case the degree of travel permitted should be included.
o
Active/Mechanical. As for Passive/Mechanical but where the movement of the lidar is
actively adjusted using powered actuation in response to sensed motions. The degree of
travel permitted should be included.
27
o
Active/Software. In this case the motion of the lidar or the platform is sensed and the
recorded wind speed and/or direction are corrected instantaneously and automatically by the
onboard software.
o
Active/Post-postprocessing. In this case the motion of the lidar or platform is sensed, but the
correction to the wind speed and/or direction is not applied automatically but as a postprocessing step.

For each of the six degrees of freedom, it should be stated whether motion compensation is applied.

For all degrees freedom for which there is motion compensation, which type of compensation is
used, and whether there are any limits outside which compensation is not applied.

In all cases where there is motion compensation using gimbals, if gimbal lock is avoided or
mitigated.

In all cases where the motion of the platform or lidar is sensed, the degrees of freedom which this
applies to and the nature of the sensors used.
RP 31: MS for lidar set-up.
The MS should include procedures for set-up, test and verification of the lidar.
3.4
POWER SYSTEM
RP 32: Provision of power systems information.

The power generation capabilities of the FLS. If renewable power sources are used, the generation
conditions for which they are qualified.

The power storage capacities of the FLS.

For all power consuming items on-board, their power consumption, including but not limited to the
lidar unit, any other sensors, the data logger, communication systems, the power systems
themselves, and navigation aids.
3.5
RP 33: Provision of data logging and communication information.

List of sensors for which measurements are recorded.

The rate at which data is logged and the quantities that are logged.

The onboard storage capacity for data. Information on planned data backups and redundancy of
data storage.

The communication systems, and protocols supported, and the rate at which data can be transferred
to shore, including the expected data rate per day.

Any aspects of the FLS control that can be managed remotely.
28
3.6
RP 34: Ancillary measurement equipment characterisation.
Besides the lidar, other atmospheric or metocean sensors may be present on the FLS, for example wave
measurement, motion detection, or atmospheric temperature or humidity sensors. Any such sensor should
be specified, the manner in which the data is gathered explained, and any required post-processing
specified.
In the case where metocean sensors are to be deployed separate to the FLS, the sensor specification and
placement requirements should be detailed.
RP 35: MS for ancillary measurement equipment set-up.
The MS should include procedures for set up, test and verification of all sensors and measurement
equipment. For each sensor, it should be explicitly stated whether any in-situ calibration or check is required.
For any such requirement, the method should be fully specified.
3.7
FLOATING PLATFORM
RP 36: Maintenance access documentation.
Provision for safe access for maintenance personnel should be fully described in the supplied data pack.
RP 37: Examples of suitable work boats.
The supplier should provide specific examples of work boats which are suitable to access the floating
platform. The examples should also detail how access is to be made, e.g. if the bow or side of work boat is to
be used. (Bow-on access as for offshore wind turbines is not generally suitable due to the inability of FLS to
withstand boat thrust.)
RP 38: Assessment of damage risk.
A review of hazards and associated risk assessment should be carried out in respect of unwanted human or
animal interference with the FLS. Mitigating actions (e.g. anti-boarding nets) should be put in place if
deemed necessary. The hazard review, risk assessment and any mitigations should be made available by
the supplier to the user.
RP 39: Specification of navigation lights.
Navigation lights should be fitted and steps taken to ensure their operation at all times. The specification of
the navigation lighting system should be included in the data pack provided by the supplier.
RP 40: Specification of geo-location system.
A geo-location system should be fitted and steps taken to ensure their operation at all times. The
specification of the geo-location system should be included in the data pack provided by the supplier.
3.8
STATION-KEEPING
RP 41: Provision of station-keeping design information.
A detailed schematic drawing of the station-keeping system, and of key dimensions and calculations
associated with the design, should be made available by the supplier. The suitability of the system for the
predicted wave, current and tidal conditions at the site should be demonstrated. For a specific arrangement,
the limitations of its suitability for subsequent deployments to other sites should be detailed (for example
29
deeper sites requiring longer tethers. Furthermore the drift radius or locus of the deployed FLS for the
specific deployment should be provided.
RP 42: Experience with the station-keeping system.
Experience during prior deployments of using the station-keeping system should be detailed by the supplier.
For example, if the planned deployment is the first for the system in question this should be clearly
communicated. Also, any problems encountered with prior deployments should be detailed, and any
remedial actions explained.
RP 43: MS for mooring.
In the case where a mooring system is used, the MS should include clear procedures, including:

Method for installing moorings (if applicable);

Method for securing the FLS to moorings;

Method for inspecting moorings;

Method for releasing from moorings;

Method for removing moorings (if applicable);
The FLS deployment should have no lasting artefacts. Any sea-bed moorings should be fully removed.
RP 44: MS for dynamic station-keeping system.
In the case where a dynamic station-keeping system is used, procedures should be detailed for the
operation of the system for the entire deployment including installation, operation, and retrieval.
3.9
RP 45: MS for transportation.
The MS should include:

The recommended means for transport of the FLS to and from the quayside.

The appropriate points on the FLS for securing during transportation.

The recommended means for temporary storage of the FLS at the quayside.

Method for any quayside assembly.

Method for lifting from quayside to on-deck or in the water at the quay.

Requirements on lifting machinery for uplift from quay.

Sea conditions in which it is safe to transport FLS from quay to intended offshore location.

For FLS systems which will be towed to site:

o
Requirements on vessel such that it is suitable for towing;
o
Safe towing speed;
o
Description of safe procedure (e.g. avoidance of capsize and excessive snatch loads).
For FLS systems which will be transported on deck:
o
Requirements on vessel such that it is suitable for on-deck transportation;
30
o
Safe transit speed;
o
Method for lifting from deck to deployment location;
o
Requirements on lifting machinery for same;
o
Sea conditions in which it is safe to perform uplift from deck.

Procedure for positioning in intended location, including detailed method for confirming orientation of
floating platform.

For recovery of the FLS, a description of lifting and/or towing requirements and methods where they
may differ from those for deployment.
31
4.
ASSESSMENT OF SUITABILITY
Before a FLS has undertaken an offshore trial, it is reasonable to expect that the system was designed to
operate reliably in the conditions likely to be encountered. FLS systems differ markedly in their conceptual
design, nonetheless it is possible to determine some recommended practices in common.
This section describes recommended practices for determining whether a candidate FLS is suitable for
deployment in an offshore FLS trial or for WRA purposes. This consists of evaluating the information
provided by the OEM (see Section 3), and refers to the OWA Roadmap [10].
For a number of the recommended practices described in this section, a distinction is made between
recommendations suitable for FLS trials and those for WRA purposes. In broad terms, for the purposes of a
FLS trial, the system should have the potential to fulfil requirements, but has not necessarily demonstrated
this ability; whereas for WRA purposes, the onus is on having substantially demonstrated capability in a
previous trial.
4.1
USING THIS SECTION
this section is useful for assessing the suitability of the candidate FLS for the intended purpose, Note that the
recommended make-up of FLS systems is described in more general terms in Section 2, which allows for an
initial assessment of suitability, however this section provides more details and is quantitative in nature
where possible.
This section should also be useful for FLS OEMs, as it provides guidance on how the FLS user will assess
the system capability.
Note that the information which is expected to be supplied by the FLS supplier, in order to enable the
assessment described in this section, is described in Section 3.
4.2
Note 11: Accuracy and availability metrics with respect to FLS maturity claims
The OWA Roadmap [10] introduced the concept of FLS maturity levels, which have been reproduced and
summarised in Table 2. These maturity levels are considered to be very useful indicators, and this
document’s recommended practices are consistent with the roadmap. To achieve “Pre-Commercial” maturity
level, accuracy and availability acceptance criteria are proposed by the roadmap that are reproduced here
(Table 3 and Table 4).
In this document, the maturity levels are extended to relate acceptance criteria for the earlier (“Baseline”)
and later (“Commercial”) maturity stages to the same accuracy and availability metrics: this is summarised in
Table 5, and further described in related sub-sections below.
Referring to Table 4, in the Roadmap the Mean Wind Direction Offset is the intercept with the y-axis. In most
circumstances this is applicable. However, in the case where the linear regression is less meaningful or may
be misleading (for example if there is a wide wake-affected sector from which data is excluded) then it may
be preferable to use the mean overall offset instead.
32
Definition
Monthly System Availability – 1 Month Average
Overall System Availability – Campaign Average
Monthly Post-processed Data Availability – 1 Month
Average
Overall Post-processed Data Availability
Acceptance Criteria
across total of six (6) months
data
≥90%
≥95%
≥80%
≥85%
Table 3: Availability/reliability Criteria from OWA Roadmap [10]. Note that availability metric definition
are described in Section 7.4.
Acceptance Criterion
Best Practice
Minimum
Definition
Mean Wind Speed – Slope
[single variant regression]
Mean Wind Speed – Coefficient of
Determination (“R-squared”)
[single variant regression]
Mean Wind Direction – Slope
[two variant regression]
Mean Wind Direction – Offset (absolute
value).
Mean Wind Direction – Coefficient of
Determination (“R-squared”)
0.98 – 1.02
0.97 – 1.03
> 0.98
> 0.97
0.97 – 1.03
0.95 – 1.05
< 5°
< 10°
> 0.97
> 0.95
Table 4: Wind speed and direction accuracy criteria from OWA Roadmap [10]. Note that applicable data
ranges and availabilities are described in Section 7.2.
Recommended
Minimum
Requirements
OWA Roadmap
Maturity Level (see
Table 2)
Availability (see Table
3)
Purpose
WRA (greater
uncertainty)
WRA (lower
uncertainty)
Baseline
Pre-commercial
Commercial
Design is fit for purpose to meet
criteria
Criteria have been
met in at least one
trial
Criteria have been met
in several independent
trials
Criteria have been
met in at least one
trial
Criteria have been met
in several independent
trials
Trial
Evidence that lidar type can
achieve criteria in a static test.
Accuracy (see
Table 4)
Design of motion compensation
or limitation is fit for purpose to
meet criteria,
Table 5: Summary of approach for wind speed and direction suitability assessment, relating to OWA
Roadmap [10] assessment criteria.
33
RP 46: Appropriate FLS maturity.
For the purposes of an offshore FLS trial, the claimed FLS maturity level should be “Baseline” according to
the OWA Roadmap [10], (Table 2). For the purposes of WRA, the claimed FLS maturity level should be at
“Pre-Commercial” according to the OWA Roadmap [10].
Note 12: Deploying a FLS at a lower maturity level
It is recognised that there may be a willingness to deploy a FLS where the maturity level is not recognised
as being so far progressed; under these circumstances the owner/operator is accepting additional risk that
the system does not perform as desired.
RP 47: Evidence of FLS maturity – wind speed and direction accuracy.
The required level of maturity differs for the purposes of FLS trials and WRA deployments.
For the purpose of an offshore FLS trial, the evidence required consists of:

Whether the lidar system itself is suitable (see Section 4.3);

An assessment of whether the floating nature of the system has been adequately accounted for in
the overall system design, in a manner which has the realistic potential to mitigate impacts (e.g. by
waves, tides, currents, mooring, water depth) on wind speed and direction accuracy (see Section
4.3);

There is no requirement to provide prior validation evidence of the accurate operation of the system
in an offshore trial.
For the purpose of a WRA deployment, the evidence required consists of:

The maturity evidence required for a FLS trial, as described immediately above;

An additional requirement to provide validation evidence on wind speed and direction accuracy from
an offshore FLS trial, which would ideally have been carried out in a manner as described in this
document, specifically referring to the trial assessment recommended practice (see Section 7).

The validation evidence should meet the criteria for a “Pre-Commercial” maturity level according to
the OWA roadmap [10], (Table 4).

It is noted that “Commercial” maturity level is attained only through multiple trials and deployments,
and entails a lower uncertainty level concerning the wind resource assessment results. The degree
to which a “Commercial” maturity level is necessary for a given WRA is a matter for judgement and
should be assessed on a case-by-case basis.
RP 48: Evidence of FLS maturity – reliability.
The required level of maturity differs for the purpose of FLS trials and WRA deployments.
For the purpose of an offshore FLS trial, the evidence required consists of:

Whether the lidar system itself is suitable (see Section 4.3);

An assessment of whether the overall system design is fit for purpose, in a manner which has the
realistic potential to survive and operate in the intended environment, with specific advice provided
below (see Sections 4.4 - 4.9);

There is no requirement to provide validation evidence of the reliable operation of the system in an
offshore trial.
For the purpose of a WRA deployment, the evidence required consists of:
34

The maturity evidence required for an FLS trial, as described immediately above;

An additional requirement to provide validation evidence on reliability from an offshore FLS trial,
which would ideally have been carried out in a manner as described in this document, specifically
referring to the trial assessment recommended practice (see Section 7).

The validation evidence should meet the criteria for a “Pre-Commercial” maturity level, as described
in Table 3.

It is noted that “Commercial” maturity level is attained only through multiple trials and deployments,
and entails a lower uncertainty level concerning the wind resource assessment results. The degree
to which a “Commercial” maturity level is necessary for a given WRA is a matter for judgement and
should be assessed on a case-by-case basis.
RP 49: Suitability of FLS Dimensions and Weight.
Confirm that the dimensions and weight of the FLS (see RP 23) are compatible with the site layout (e.g.
available space at quayside, water depth at low tide and including wave action, weight limitation of lifting
equipment, permissible drift radius when deployed).
RP 50: Suitability of operating conditions.
It should be confirmed that the range of metocean and wind conditions that the supplier asserts the FLS is
capable of operating in (see RP 24) is consistent with the expected conditions at the site. This should include
consideration of the impact of extreme conditions. (Note that assessing whether accuracy is sufficiently likely
to be acceptable under expected conditions is addressed by RP 57).
RP 51: Suitability of maintenance information and regime.
The information supplied on maintenance requirements and the maintenance regime should be reviewed for
fitness-for-purpose by suitably qualified and experienced staff. It is recommended that the scheduled
maintenance interval during deployment, including for replenishment of consumables, should be greater than
6 months.
RP 52: Suitability of Method Statement (MS).
The information supplied in the MS on how to deploy, commission, recover the FLS, and on how to perform
component replacements, should be reviewed for fitness-for-purpose by suitably qualified and experienced
marine operations staff. The MS should also detail operational procedures for dropped objects, emergency
response and risk register.
RP 53: Protection from damage due to relative motion – power system.
Where there is relative motion between parts of the FLS, care should be taken to protect any component
(e.g. data and power connectors) which may be exposed to wear.
Note 13: Oversizing components and reducndancy
A general observation is that oversizing the capacity of systems (e.g. power generation, power storage, data
storage, communication redundancy) and added redundancy with respect to the expected demands on them
is an effective design policy promoting resilience of the system.
RP 54: Overall system evaluation – general.
The fitness-for-purpose of the overall system (including power systems, communications, data logging,
ancillary measurement equipment, mooring, compatibility of work boats) and its transportation should be
evaluated by a suitably qualified and experienced expert individual or organization, taking account of
recognised risks (see Note 3, Note 7, Note 8).
35
4.3
LIDAR SYSTEM
RP 55: Evaluating accuracy of the lidar type.
The type of lidar device used in the FLS shall have been tested in several well-documented tests prior to its
integration. These onshore tests shall have been performed according to the guidelines in IEC 61400-12-1
CD2 (see [11]), and the IEA Wind Recommended Practices for ground-based lidars [5], respectively, and the
results shall be available to the user of the FLS. The results will be available as one or two parameter linear
regressions in a good quality, peer-reviewed publication or otherwise be endorsed independently by qualified
and experienced individuals. The level of accuracy demonstrated in these tests will be at least within the
acceptance criteria for wind speed and accuracy from Table 4. It is accepted that due to the specific details
of the tests carried out, the metrics obtained may not be directly comparable with those in Table 4 however
this is a useful guide.
RP 56: Wind industry acceptance of the lidar type.
The lidar type should have been used commercially for WRA purposes (e.g. for onshore projects, and/or
offshore deployments on fixed platforms). Types that are considered by the manufacturer to be appropriate
for operation in a marine environment, but have not been demonstrated in a marine environment, should be
considered as inherently more risky.
Note 14: Evaluation of motion compensation – general.
There is a risk that the motion compensation or limitation arrangements on the FLS are not sufficient to avoid
problematic deterioration of the wind speed and/or direction measurement accuracy. The evaluation can
include design information, modelling data and trial data.
RP 57: Evaluation of motion compensation – FLS trial.
It is recommended that for an FLS trial deployment, there is convincing evidence that the motion
compensation system has the potential to work effectively in the range of sea states to be encountered
during the trial, the evidence provided to justify this potential should be reviewed by a suitably qualified
person. Note that the range of motions experienced during the trial will be monitored and checked (Section
5.5 and 7.3).
RP 58: Evaluation of motion compensation – WRA deployment.
It is recommended that for an FLS deployment for WRA, there is convincing evidence that the motion
compensation system has been demonstrated to work effectively in the range of sea states to be
encountered during the deployment. Ideally this demonstration is in the form of an offshore FLS trial, which
would have been carried out in the manner described in this document, specifically referring to the trial
assessment recommended practice (see Section 7). As for FLS trials, each degree of freedom should be
considered separately and evidence provided that the motion compensation (or justification for lack of motion
compensation) has the potential to be sufficient; however in this case this should be supplemented by
specific trials data. Ideally the range of sea states encountered in the trial would encompass the extremities
of the range of sea states anticipated in the WRA deployment; also the trial deployment period would be as
recommended (see Section 7). The degree to which a lesser range of sea states and/or a shorter trial
deployment period can be accepted is dependent on the owner/operator’s appetite for risk, and the
acceptability level should be considered in this light.
36
4.4
POWER SYSTEM
RP 59: Power storage requirement.
It is to be expected that the FLS will have to operate for some periods without any on board renewable
power sources generating power. It is therefore recommended that there is reserve power (e.g. in the form of
batteries) for the system to operate fully for at least 1 week, and preferably for 2 weeks.
RP 60: Power system maintenance/replenishment requirement.
The maintenance interval recommended practice (see RP 51) implies that the power system should be able
to operate autonomously for at least 6 months without replenishment (e.g. for fuel cells) or maintenance.
This should be confirmed,
RP 61: Power system full recharge requirement.
Renewable power systems should be sized to provide a complete recharge of batteries, rather than just a
top-up charge.
Note 15: Safe access to power system components.
Where wind charger units are deployed, consideration should be given to safe access for personnel, either
by suitable location and guarding and/or by the use of shorting/furling procedures.
The safety of batteries should also be considered, especially the explosion risk caused by the use of lead
acid batteries. Suitable ventilation systems and safe methods of inspection and access should be provided.
4.5
RP 62: Evaluating data logging capacity.
There should be sufficient data storage on-board to ensure that all data measured for the duration of the
deployment is stored and recoverable after the trial, in the event that communication fails.
RP 63: Evaluating communication system redundancy.
The communication system should include at least two separate means of communication (e.g. through both
satellite and 3G cell network communications). The type of communication used should switch automatically
or otherwise be controllable without deploying personnel offshore.
RP 64: Evaluating communication system – wireless system.
A wireless communication system should be in place, such that a connection can be established from a
workboat approaching but not necessarily attaching to the FLS. The wireless communication system should
feature, as a minimum:
4.6

The full range of data download and control features available in normal offshore/onshore
communication;

A reset capability for the lidar, logging system, communication system and power system.
RP 65: Evaluating metocean sensor set-up.
Metocean sensors capable of recording at least wave height and wave frequency over no longer than 30
minute intervals must be part of the FLS or recommended to be deployed separately as part of the
measurement campaign. If the metocean sensor is mounted on the buoy, a careful evaluation of whether the
presence of and motion of the buoy could have a deleterious effect on the metocean sensor should be
37
made. For separate metocean measurement systems deployments, the separation distance should be no
more than 500m. The specific metocean characteristics which should be available are those also specified in
Section 5.5.
RP 66: Evaluating secondary wind speed and direction sensors.
A secondary source of wind speed and direction measurement should be available as a cross check. An
anemometer and a wind vane at approximately platform level (or ideally at the standard 10m reference
level), and free enough from obstruction to function as a functionality check, would be sufficient for example.
Note 16: Evaluation of inclinometers and other motion sensors – general.
Depending on the type of FLS, it may be advantageous to provide information on the inclination and/or
orientation of the lidar. For example, if the FLS has been demonstrated to have good accuracy in moderate
sea states, it may be advantageous to monitor the range of inclinations experienced (or rate of change of
inclinations) for a new deployment in heavy sea states. No recommendations for monitoring are made.
However the following may be considered:
4.7

For a spar-buoy system which is not designed to incline by more than a few degrees, monitoring the
maximum inclination recorded every 10 minutes;

For a marine buoy where assumptions are made on the maximum angular rotation which is tolerable
to maintain wind speed measurement accuracy, monitoring the inclination at 10Hz and from this
deriving the maximum angular rates experienced;

For a buoy where the wind direction is in part derived from the orientation of the FLS relative to a
global reference frame, monitoring the orientation of the FLS at 1Hz.
FLOATING PLATFORM
RP 67: Evaluation of the floating platform – safety systems
The provision for safe access, conducting offshore maintenance tasks, risk assessment, navigation lights
and geo-location system should be assessed by a suitably qualified and experienced expert individual or
organization. The expert should also assess the presence and fitness for purpose of any other applicable
safety systems or process.
4.8
MOORING
RP 68: Evaluation of mooring arrangement suitability for site.
Even if a FLS has been successfully deployed before, it is not necessarily the case that the same
combination of buoyancy, mooring cable length and FLS dimensions will be successful at another site with
different seabed conditions, current, tide and depth characteristics. For this reason the suitability of the
mooring arrangements should be reviewed for each proposed new site by a suitably qualified mooring
design authority.
RP 69: Evaluation of MS for mooring inspection.
Moorings should be visually inspected from anchor to fairlead annually. This inspection can identify worn
links, line abrasions, and other damage.
38
4.9
RP 70: De-risking shock damage to the lidar
If the lidar is transported as an integral part of the FLS then the FLS should be fitted with one or more shock
sensors during transportation to the site to detect events that may damage equipment. A shock sensor
should be affixed directly to the lidar unit to detect events that may damage the lidar. In each case an agreed
acceptable acceleration threshold should be agreed between the supplier and the owner/operator prior to
transportation. Where mechanical motion compensation is used the motion compensation should be
disabled during transportation to reduce the chance of unexpected motion.
39
5.
TRIAL CAMPAIGN DESIGN
5.1
OVERVIEW
This section describes recommended campaign parameters for the case where the purpose of the
deployment is to trial a FLS, and refers to the OWA Roadmap [10]. Note that this is distinct from an FLS
deployment for the purpose of Wind Resource Assessment (WRA), see Section 6. The assumed purpose of
the trial is to assess the capability of the FLS to accurately and reliably measure wind speed and direction.
This necessitates the use of a trusted reference measurement system for wind speed and direction.
Specification for recommended reference measurement systems is included in this section.
This section is structured as follows:

Confirming correct and accurate operation of equipment prior to deployment on a trial is described in
Section 5.2.

A discussion of a suitable location for the trial is included as Section 5.3.

The recommended equipment and facilities are described in 5.4. This includes the reference wind
speed and direction measurement system, and a metocean measurement system.

The quantities which should be measured are described in Section 5.5.

Recommended functionality checks to avoid the risk of using damaged or poorly operating
equipment are described in Section 5.6.

Data monitoring which should be performed during the trial is described in Section 5.7.

Confirming that measurement equipment has not deteriorated after the trial is described in Section
5.8.
Note that the closely related topic of performing the comparison between FLS wind data and those from the
reference system (as well as a consideration of availability) is described in Section 7.
RP 71: ‘Blind’ trial principle.
To avoid any doubt on the integrity of the trial, the suppliers of the FLS system or any other actors in its
deployment should ideally not have any visibility of data from the reference system until FLS data have been
supplied to the adjudicator for the equivalent period. This may not always be possible, in which case
independent measures should be taken to verify integrity of the reference data, FLS data, and the
comparison of the two data sets.
RP 72: Feedback on performance
The FLS supplier should have access to the FLS data throughout the campaign, without violating the blind
trial principle. Feedback from the reference system should be provided during the first two weeks of
deployment and at regular intervals throughout the campaign to ensure that the FLS is performing as
expected.
5.2
PRE-DEPLOYMENT CHECKS
The guidelines in IEC 61400-12-1 CD2 / Annex L [11] should be followed to establish confidence in the
accuracy of the lidar unit to be used in the FLS trial:

The lidar is tested against a measurement mast equipped with standard anemometry.
40

Based on the collected measurement data, a verification test or accuracy assessment is performed.

The verification test shall be performed for each individual system before application in the trial. A
system classification is necessary only for each type of system, as specified in IEC 61400-12-1 CD2
[11].
Note that these IEC guidelines do not in themselves provide acceptance criteria for the unit under test, rather
they are guidelines for the manner in which the verification check should be conducted. For this reason, it is
useful to supplement these guidelines with data coverage criteria from the NORSEWInD trials [12] and
accuracy acceptance criteria from the OWA roadmap [10] as shown in Table 4.
5.3
LOCATION
RP 74: Ideal location for a FLS trial
The location for a FLS trial has the following recommended characteristics:

Minimal variation in the wind resource across the site, to facilitate comparison of measured data from
the FLS and the reference system;

A similar wind and metocean climate to the target site or sites for subsequent WRA deployment of
the FLS.
Note 17: Ideal location for a FLS trial
It is not always possible to carry out a trial in an ideal location. Non-ideal circumstances can include, for
example, a suspected variation of wind resource across the site due to coastal effects, or relatively benign
wind and metocean conditions compared to the target site for WRA deployment. In such cases, it is likely
that a worthwhile FLS trial can still take place, but that care must be taken in interpreting the data, and there
is likely to be an increased uncertainty compared to the ideal case.
5.4
EQUIPMENT AND FACILITIES
Note 18: Reference system for wind speed and direction.
The reference system for wind speed and direction could be an offshore met mast, or any other trusted
reference measurement system mounted as the situation allows, for example: onshore met masts or lidars;
met masts or lidars on piers, lighthouses, or other offshore structures, etc. The key concern is the uncertainty
in the wind speed and direction measurement, which should be at an acceptable level (as assessed by a
suitable expert). It should be noted that the uncertainty of the FLS measurements derived from the trial
results cannot be lower than the uncertainty of the reference system measurements. IEC 61400-12-1 CD2
Annex L details a method for determining absolute uncertainty [11]
RP 75: Specification of the reference system.
Specifications and associated data for the reference system must be available. The effects of the mast
structure, foundations and platforms or other flow distorting features on the reference measurements should
be well understood and documented (for example mast and boom effects, possible effects of the substructure and platform). Furthermore, the influence of the site itself (e.g. topography) on reference
measurement uncertainty should be well understood.

Mechanical and ultrasonic anemometry systems should be designed and installed in accordance
with IEC 61400-12-1 [2]. The measuring instruments (anemometers and wind vanes) should be
suitably calibrated by an accredited calibration laboratory within the last 12 months.
41

It is recognised that the OWA roadmap [10] does not refer to the use of other reference systems,
namely remote sensing devices, as suitable. Here it is considered that technology maturity has
developed sufficiently to consider remote sensing devices as suitable references, assuming that the
measurement campaign is carried out by suitably qualified and experienced experts or
organisations.

For the case of other reference systems, industry best practice for set-up should be followed; if the
reference systems are lidars then the guidelines in references [5] and [11] should be followed. In that
case it is important that the equipment and power supply be such that the reference lidar may
operate for extended periods without disturbance and interruption in highly challenging environments
and that the influence from the support structures (for offshore platforms) or from the ground (onshore/ near-shore installation) on the reference instrument are negligible or well understood.
RP 76: Separation distance between FLS and reference system.
To achieve a high comparability between the FLS and reference measurements, the separation distance
should be minimised, while respecting the relevant safety restrictions. In general a separation direction
aligned with the prevailing wind is preferred to a separation direction which is transverse to the prevailing
wind. In past trials a separation distance of 500m has been used successfully so this is the current
recommendation. It is considered that if a separation distance of less than 500m were used in a wellconfigured trial, poor agreement between reference and FLS data would not be attributed to too small a
separation distance. Conversely, for greater separation distances it is unlikely that doubt would be
introduced to trial results in good agreement; however trial results in poor agreement would be difficult to
attribute to large separation distances or other factors.
RP 77: Positioning to ensure undisturbed flow.
Both the FLS and the reference system should be subject to an undisturbed flow, i.e. a valid measurement
sector shall be defined in a way that neither the measurements of the FLS nor those of the reference system
are affected by wakes of surrounding wind turbines or other obstacles.
RP 78: Metocean measurement system.
Measurements of the oceanographic conditions should be made sufficiently close to the FLS under test such
that they are representative. These should be taken using an industry accepted and time proven system
which has been suitably maintained and calibrated in line with the manufacturer’s guidance.
RP 79: Ancillary measurement system.
If supplementary measurements are required as part of the validation process (such as air temperature,
humidity, barometric pressure etc), instrumentation must be installed and operated in line with the
manufacturer’s guidelines and industry best practice. Instruments must have been calibrated by an
accredited calibration laboratory and remain in calibration for the period of the trial.
RP 80: Synchronisation of data loggers.
Data loggers on the FLS and reference system should be time synchronised to a common public source
(such as GPS time, radio signal, or other global reference source), such that an offset or drift between the
FLS and the reference system throughout the course of the trial is minimised (e.g. 10 seconds is acceptable)
.
42
5.5
MEASURED QUANTITIES
The quantities of most fundamental importance are wind speed and direction. At the simplest level, the
accuracy of the FLS will be assessed by comparing the wind speed and direction measurements from the
FLS with those from the reference system, and the reliability of the FLS as a measurement device will be
assessed on the availability of these data.
RP 81: Measured Quantities - Datum.
For all quantities which are made at a specific height, including wind speed and direction, the height should
be reported as well as the datum used, for example mean sea level.
RP 82: Measured Quantities - Comparison.
The FLS and the reference system should measure wind speed and direction at a range of heights as
follows:

Wind speed (m/s) should be recorded as a 10 minute average;

Wind direction (degrees) should be recorded as a 10 minute average.
In addition, it is recommended to also record minimum, maximum and standard deviation values, within
these 10 minute periods, for these quantities. This presents an opportunity to investigate turbulence
measurements and to perform additional functionality checks.
It is further good practice to publish the amount of data measured in each of the data bins and to report the
amount and location of any data that has been excluded through post-processing or filtering.
Note that the above is consistent with the OWA roadmap [10].
RP 83: Measured Quantities - Sensitivity.
Other quantities are used to assess the sensitivity of the wind speed and direction correlations to site
conditions. The quantities that should be measured for this purpose include:

Significant and maximum wave height (m) ) should be recorded as a 30 minute average;

Peak and mean wave period (s) should be recorded as a 30 minute average.
Also, tide height (with respect to MSL) should be available for the trial site and the duration of the trial, noting
that this is often available from sources not related directly to the trials equipment. It is also recommended to
record a number of other environmental and FLS-related quantities for the purposes of sensitivity analysis. It
is not possible to generalise further as their importance or otherwise will depend on each case; for example,
for a FLS which is designed to isolate the lidar from angular motions, it may be important to measure the
motion of both the buoy and of the lidar if there is a lack of other substantiation. Such quantities where it is
advisable to consider taking measurements are as follows:

Inclination (pitch, roll, yaw) of the platform (and of the lidar if isolated or compensated from the
platform motion);

Translational accelerations (heave, surge, sway) of the platform (and of the lidar if isolated or
compensated from the platform motion);

Rotational accelerations (rate of change of pitch, roll, yaw) of the platform (and of the lidar if isolated
or compensated from the platform motion);

Current speed;

Air and water temperature;

Humidity;
43

Cloud cover, mist/fog, visibility;

Precipitation.
Lastly, as described in Section 2.3, lidar quality criteria may be provided in a manner such that the end user
can apply a variable quality threshold, e.g. to CNR. In such a case it is recommended to perform a sensitivity
study with respect to available variable quality criterion thresholds.
Note 19: Measurement heights for wind speed and direction in a trial.
Ideally, wind speed and direction as measured by the FLS and the reference system will be compared at a
number of heights within a range equivalent to a contemporary large turbine’s rotor disk minimum and
maximum heights, and including the hub height. It is recognised that this may not be practically possible, and
that a smaller range may still result in very useful trial data. However, if as a minimum the hub-height level
cannot be attained, this is far from ideal as this introduces a significant degree of uncertainty: firstly, hubheight wind speed is still seen by the industry as the key parameter, and a vertical extrapolation would have
to be performed to estimate the wind speed at hub height; second, for some systems potential sources of
inaccuracy due to FLS motion may be a function of beam length/height, and may not become evident for
short beam lengths/lower heights.
RP 84: Recommended measurement heights for wind speed and direction in a trial.
The reference system should measure wind speed and direction at a range of at least four heights, with a
maximum not less than hub-height of a contemporary large turbine; one of the measurement heights should
be equivalent to hub-height. As measuring shear is of interest it is advisable to set up the lowest
measurement height to be the minimum height achievable given the practical limitations e.g. the combination
of measurement platform height and minimum lidar beam height is likely to dictate this. Hub-height minus
20m is generally acceptable as a height from which useful shear measurements can be made. The ranges of
the lidar on the FLS under trial should be configured to match these heights, with MSL as the reference
height.
RP 85: Recommended trial duration.
A six-month trial duration is recommended for the following reasons:

This should provide adequate data coverage to perform a meaningful correlation of wind speed and
direction measurements.

A more demanding requirement in terms of data coverage is that pertaining to metocean conditions;
it is considered likely that a representative range of conditions may not be attained for a shorter trial
duration.

A WRA deployment is likely to last for more than six months. Therefore the system should
demonstrate its reliability for at least six months.

It is recognised that accuracy and reliability aspects of the FLS should ideally be trialled
simultaneously.

The most straightforward way to meet all of these considerations is for a single six-month trial period.
However it is recognised that a six-month trial is not always practical to achieve, and accuracy and reliability
evidence from some other combination of trial deployments may be considered as equivalent. However this
evidence should be considered and justified on a case-by-case basis.
44
5.6
FUNCTIONALITY CHECKS
Note 20: Functionality checks at the outset of a trial
There is significant risk that in transportation or installation some damage or misalignment of the
measurement systems occurs. Therefore the trial procedures should include checks of the correct operation
of all systems immediately after deployment to the final trial location and switching on. The FLS supplier
should include such procedures for their own systems as part of the Method Statement. Equivalent
procedures should be in place for the reference system and ancillary measurement equipment (which is
likely to be the responsibility of the trial operator rather than the FLS supplier). Note that these functionality
checks should not violate the principle of the “blind” trial.
5.7
MONITORING DURING DEPLOYMENT
Note 21: Regular monitoring during trial.
Experience has shown that it is prudent to regularly monitor a FLS during deployment so that any problems
that emerge can be remedied at the earliest opportunity.
RP 86: Recommended monitoring during trial.
The following monitoring of the FLS is recommended during the trial:

Data availability.

For the indicated wind speed and direction, that they are realistic values.

The functioning of the on-board power system e.g. voltage levels in any batteries, and/or evidence of
renewable power sources being effective.

Any available lidar data quality criteria (e.g. CNR, spatial variation, etc.)

Location of the FLS to check it is within the expected drift radius.
It is recommended that such checks are performed on a daily basis in the first two weeks of deployment, and
subsequently on a weekly basis as a minimum. This monitoring should form part of the maintenance
management plan for the FLS and should include alerts that will trigger reactive interventions.
5.8
POST-DEPLOYMENT CHECKS
Note 22: Post-deployment checks.
Once a lidar unit has been established as sufficiently accurate (see Section 5.2), there is no clear reason for
suspecting that its accuracy will degrade in a systematic manner during the trial in a manner that would
compromise the trial results. Therefore it is not normally recommended to perform a post-trial verification
check on the lidar unit. Circumstances which may result in a decision to perform a post-trial validation are for
example if a doubt has arisen through an accident or impact affecting the lidar during the trial.
45
6.
WIND RESOURCE ASSESSMENT CAMPAIGN DESIGN
6.1
OVERVIEW
This section describes recommended campaign parameters for the case where the purpose of the
deployment is to support wind resource assessment. Note that this is distinct from an FLS deployment for the
purpose of trialling a FLS (see Section 5). Many of the recommendations are the same or related to those
presented in Section 5. In this section it is also recommended to use a trusted reference measurement
system for wind speed and direction; however in this case this is for a shorter duration as part of predeployment checks, rather than as the primary purpose of the FLS deployment.
This section is structured as follows:

Confirming correct and accurate operation of equipment prior to deployment on a trial is described in
Section 6.2.

A discussion of a suitable location is included as Section 6.3.

The recommended equipment and facilities are described in 6.4. This includes the reference wind
speed and direction measurement system, and a metocean measurement system.

The quantities which should be measured are described in Section 6.5.

Recommended functionality checks to avoid the risk of using damaged or poorly operating
equipment are described in Section 6.6.

Data monitoring which should be performed during the trial is described in Section 6.7.

Confirming that measurement equipment has not deteriorated after the trial is described in Section
6.8.
Note that the closely related topics of performing the comparison between FLS wind data and those from the
reference system for the pre-deployment check (as well as a consideration of availability), and assessment
of the wind data itself, are described in Section 8.
The blind trial principle, which is described in Section 5.1 for FLS trials, also applies here for the predeployment check of the FLS.
6.2
PRE-DEPLOYMENT CHECKS
The recommendation is equivalent to that for FLS trial deployments (Section 5.2).
RP 88: Requirement for and duration of pre-deployment verification check on FLS unit.
It is assumed that the FLS type that is to be deployed for WRA purposes is of a type which has previously
been the subject of an offshore trial (see Section 5). The purpose of the pre-deployment check for the FLS
unit to be used is not therefore to establish that the type is capable of good performance – this has already
been established. Rather, it is to establish confidence that the specific unit is as good as the one which was
trialled. It is recommended that the nature of the pre-deployment check is the same as the full-scale FLS trial
described in Section 5. However, having the same duration of trial is judged as being excessive. Deciding on
an appropriate duration is a matter for expert judgement and is system and situation dependent. An
expected minimum requirement on duration is that there is sufficient population of wind speed bins to
perform a meaningful correlation (see Section 8.2), as well as coverage of expected sea states. If there is
46
sufficiently strong evidence of system maturity with respect to stability and/or motion compensation, or
sufficient other justification providing confidence in these factors, then the required duration may reduce. The
purpose of the pre-deployment check is to de-risk the specific unit not performing to the same standard as
the previously-trialled unit, so judgement should focus on the risks pertaining to the specific system and unit
and their mitigation.
6.3
LOCATION
The location of the deployment for WRA is determined by project requirements.
Note 23: Ideal location for FLS pre-deployment check (prior to WRA deployment)
The location is subject to the same consideration as for the FLS trial (Section 5.3). In addition, the location
should be such that subsequent transport to the WRA site can be carried out with minimal disturbance to the
FLS system. Note that even with a pre-deployment check there is still in principle a risk that the system will
not perform as well at the WRA location as it did at the pre-deployment check location due to factors which
have to be changed or tuned between locations (e.g. the tuning for gimbals, mooring systems). As far as
possible the FLS should have the same set-up at the pre-deployment site as it does at the WRA site. Every
deviation from this, due to differences in location attributes or otherwise, should be recorded and justified.
6.4
EQUIPMENT AND FACILITIES
The considerations and recommendations for equipment and facilities are as for the FLS trial (see Section
5.4), with the observation that in this case the reference system pertains to that used in the pre-deployment
check.
6.5
MEASURED QUANTITIES
The considerations and recommendations for measured quantities are the same as for the FLS trial (see
Section 6.5), with the following distinctions:
6.6

In this case the reference system means the reference system used in the FLS pre-deployment
check.

The duration of the pre-deployment check of the FLS is a matter for expert judgement (see Section
6.2).

The duration of the deployment for WRA is determined by project requirements.
FUNCTIONALITY CHECKS
The considerations and recommendations for functionality checks are as for the FLS trial (see Section 5.6).
6.7
MONITORING DURING DEPLOYMENT
The considerations and recommendations for monitoring during deployment are as for the FLS trial (see
Section 5.7).
47
6.8
POST-DEPLOYMENT CHECKS
RP 89: Post-deployment checks – lidar unit
It is not generally recommended that the pre-deployment check for the lidar unit (see section 5.2) should be
repeated after the WRA deployment, despite this being inconsistent with MEASNET advice (see Annex C of
[13]). An exception to this would be if for any reason doubt has arisen on the lidar unit performance during
the trial.
Note 24: Post-deployment checks – FLS unit
It is not normally necessary to perform a post-trial verification check on the FLS unit. Circumstances which
may result in a decision to perform a post-trial validation are for example if a doubt has arisen through an
accident or impact affecting the FLS during the trial. Also see 5.8.
48
TRIALS RESULTS ASSESSMENT
7.
Section 5 describes recommended practices for trialling a FLS. Having carried out such a trial, the question
arises as to how to best assess the results. This section describes the required data processing and
comparisons and also relevant compliance and acceptance thresholds. This section also refers to the OWA
Roadmap [10].
7.1
INDEPENDENCE OF RESULTS ANALYSIS
RP 90: Independence of trial results
The FLS trial and the results of the data analysis should be reviewed by a suitably skilled and experienced
independent organisation in order for the trial to be credible. This review should include verification of the
correct execution of the measurement campaign design, and review of data capture and analysis.
7.2
WIND SPEED AND DIRECTION ACCURACY
RP 91: Wind speed and direction correlations
Wind speed and direction accuracy will be assessed using correlations of FLS and reference measurement
system data. Only data from pre-defined sectors with undisturbed flow should be used, see RP 77. Only
post-processed data qualified as “good” by the system should be used, after application of quality filters
defined by the lidar supplier. Ten minute averaged data will be used, and an ordinary least-squares linear
regression created. Each valid wind speed data point from the FLS will be cross-correlated with the
equivalent reference measurement system data (i.e. with the equivalent time stamp). For wind speed
correlations the y-intercept will be set to zero (i.e. a single-variant regression of the form y=mx). For wind
direction correlations the y-intercept will be permitted to be non-zero (i.e. a two-variant regression of the form
y=mx+c). Examples are shown in Figure 2 and Figure 3. Correlations should be produced in this way for the
following data:


Wind speed:
o
All wind speeds >2m/s;
o
Wind speeds in the range [4 – 16] m/s;
o
o
o
Wind speeds in the range [12 – 16] m/s.
Wind direction:
o
All wind directions, all wind speeds >2m/s.
In creating wind direction correlations, care should be taken to manage “wrap-around” data points correctly.
For example, if at a certain time a wind vane on a mast records a wind direction of 1º, and the FLS records
364º, it is advised to translate the latter value to -1º before evaluating the correlation.
49
RP 92: Data coverage requirements for wind speed and direction correlations
There is a minimum requirement on the data coverage required to achieve a meaningful correlation. At least
40 data points are required in each 1m/s bin between 2 m/s and 12 m/s, and at least 40 data points are
required in each 2m/s bin between 12 m/s and 16 m/s.
RP 93: KPIs for wind speed and direction accuracy
The Key Performance Indicators (KPIs) for wind speed and direction accuracy are the coefficients returned
from the ordinary least-squares regressions performed on the data, as summarised in Table 4.
(a) See Reference 8.
(b) See Reference 14.
(c) See Reference 6.
(d) Above figure provided by J Gottschall, related
to Reference 9.
Figure 2: Examples of wind speed correlations from various sources. (Note that the recommended
practice is to use single-variant regression, whereas these figures also show two-variant
regressions.)
50
(a) See Reference 8.
(b) See Reference 14.
Figure 3: Examples of wind direction correlations from various sources
7.3
SENSITIVITY OF WIND SPEED AND DIRECTION ACCURACY RESULTS
RP 94: Sensitivity of wind speed and direction error
The error associated with each wind speed and direction data point comparison will be calculated and
plotted against the parameters listed below:

Wind speed and wind direction;

Significant and maximum wave height;

Peak and mean wave period;

Wave steepness (which can be derived from wave height and period).
In addition, the sensitivity of the wind speed and direction error will also be calculated and plotted against
any other parameters which were deemed to be significant in the design of the trial (see Section 5.5). Some
examples are shown in Figure 4 below.
51
(a) Example of wind speed error sensitivity to
significant wave height (Reference 8).
(b) Example of wind speed error sensitivity to
wind speed (Reference 14).
(c) Example of wind speed error sensitivity to wave
height (Reference 6).
(d) Example of wind speed error sensitivity to
wind speed (Reference 9).
Figure 4: Examples of wind speed error sensitivity to different factors from various sources
7.4
AVAILABILITY
The following availability definitions are used as KPIs:

Monthly System Availability: One-Month Average.
o
The FLS is ready to function according to specifications and to deliver data, taking into
account all time stamped data entries in the output data files including flagged data (e.g. by
NaNs or 9999s) for the given month. Note that for the system to be considered “ready”, at
least one valid data point must be recorded (at any height).
52
o


Overall System Availability: Campaign Average
o
The FLS is ready to function according to specifications and to deliver data, taking into
account all time stamped data entries in the output data files including flagged data (e.g. by
NaNs or 9999s) for the pre-defined total campaign length. Note that for the system to be
considered “ready”, at least one valid data point must be recorded (at any height).
o
The Overall System Availability is the number of those time stamped data entries relative to
the maximum possible number of (here 10 minute) data entries including periods of
maintenance within the pre-defined total campaign period.
Monthly Post-processed Data Availability: One-Month Average
o
o

The Monthly Overall System Availability is the number of those time stamped data entries
relative to the maximum possible number of (here 10-minute) data entries including periods
of maintenance within the respective month.
The Monthly Post-processed Data Availability is the number of those data entries remaining

after system internal (unseen) filtering (e.g. -22dB CNR filter), i.e. excluding (NaN or
999) flagged data entries,

and after application of quality filters based on system own parameters, to be
defined and applied in a post processing step on the basis of lidar contractor
guidelines,
relative to the maximum possible number of (here 10-minute) data entries within the
respective month, regardless of the environmental conditions within this period. Note that
there should be a data availability value for each measurement height.
Overall Post-processed Data Availability
o
o
The Overall Post-processed Data Availability is the number of those data entries remaining

after system internal (unseen) filtering (e.g. -22dB CNR filter), i.e. excluding (NaN or
999) flagged data entries,

and after application of quality filters based on system own parameters, to be
defined and applied in a post processing step on the basis of lidar contractor
guidelines,
relative to the maximum possible number of (here 10-minute) data entries within the predefined total campaign period regardless of the environmental conditions within this period.
Note that there should be a data availability value for each measurement height.
A number of other KPIs relating to availability and reliability should be recorded from the trial data. These are
defined as follows, and are taken from the OWA Roadmap document [10]:

Number of Maintenance Visits. Number of visits to the floating lidar system by either the supplier or
an authorised third party to maintain and service the system.

Number of Unscheduled Outages. Number of unscheduled outages of the floating lidar system in
addition to scheduled service outages. Each outage needs to be documented regarding possible
cause of outage, exact time / duration and action performed to overcome the unscheduled outage.

Uptime of Communication System. To be documented and reported by the supplier.
53
7.5
ACCEPTANCE CRITERIA
RP 97: FLS trial results acceptance criteria – accuracy
Having performed an analysis of wind speed and direction accuracy according to Section 7.2, suitable
acceptance thresholds for accuracy are summarised in Table 4.
RP 98: FLS trial results acceptance criteria - availability
Using the availability definitions from Section 7.4, suitable acceptance thresholds for availability are
summarised in Table 5.
7.6
ASSESSMENT OF UNCERTAINTY OF FLS MEASUREMENTS
Note 25: Considerations on the FLS measurement uncertainty budget
The uncertainty budget of the FLS measurements in the final application – as e.g. part of a wind resource
assessment campaign (see Sections 6 and 8) – is made up of different uncertainty components as detailed
in [15]. These components can in part be derived from the results of an FLS trial described in Section 5. The
listing includes the following components:

Reference uncertainty, i.e. the uncertainty of the measurements of the reference met. mast –
guidelines on its estimation is given in the same standard document;

Uncertainty resulting from performance verification test (details below);

Uncertainty due to system classification (details below).
Furthermore, it is assumed that the uncertainties due to non-homogenous flow within the measurement
volume, due to mounting effects and due to variation in flow across the site are not relevant for a typical FLS
trial set-up and its evaluation.
RP 99: Assessment of uncertainty resulting from performance verification test (from FLS trial
results).
An uncertainty resulting from performance verification test, that is part of an FLS trial as outlined in Section
5, should be derived following the procedure in Annex L.4.2 of IEC 61400-12-1 CD2 [15].
Since the reference uncertainty typically dominates this uncertainty, it is recommend to compare the
deviation between FLS and reference measurement with this value bin-wise – cf. Figure L.7 in IEC 6140012-1 Ed. 2 CDV.
Note 26: Assessment of uncertainty due to system classification (from FLS trial results).
The concept of an FLS classification test is beyond the scope of this document and may be an issue of
future work in this field. The same applies to the definition of a respective classification uncertainty as in IEC
61400-12-1 Ed. 2 CDV L.4.3. The sensitivities investigated according to RP 83 may build a basis for a first
assessment. If a significant sensitivity to one of the investigated parameters is found, its maximum impact
may either be already covered by the verification uncertainty, or be considered as an additional uncertainty
associated to the related risk.
54
7.7
LESSONS LEARNT
The opportunity to learn from experience during a FLS trial, ahead of a “real” deployment e.g. for wind
resource assessment purposes, is considerable. It is recommended that there is a formal “lessons learnt”
activity involving all stakeholders on completion of a trial. The scope of the activity should include all aspects
including planning, procurement, deployment, maintenance, recovery as well as system accuracy and
reliability. Where possible and acknowledging commercial sensitivities, details of lessons learnt should be
disseminated to the offshore wind industry in general.
55
8.
WIND RESOURCE ASSESSMENT
Section 6 describes recommended practices for using a FLS for wind resource assessment purposes.
Having carried out measurements in this way, the question arises as to how to best assess and use the
results. This section describes the required data processing and comparisons and also relevant compliance
and acceptance thresholds.
Note that this section is not prescriptive on how to use FLS wind data in a wind resource assessment, rather
provides guidance on methods to assess the data quality using a FLS. See Section 1.5 for more information
on limitations of the recommended practice.
8.1
INDEPENDENCE OF RESULTS ANALYSIS
RP 101: Independence of pre-deployment checks and results analysis
Any pre-deployment verification, of the lidar unit or the FLS system (see Section 5.2) should be reviewed by
a suitably skilled and experienced independent organisation in order for the campaign outcomes to be
credible. This should include verification of the correct execution of the pre-deployment check design.
8.2
WIND SPEED AND DIRECTION ACCURACY
RP 102: Wind speed and direction correlations: pre-deployment check
The wind speed and direction accuracy of the FLS during the pre-deployment check should be assessed as
described for a dedicated FLS trial in Section 7.2 (if a pre-deployment check has been carried out).
RP 103: Data coverage requirements for wind data correlations: pre-deployment check
The data coverage achieved should be assessed against the requirements: it is expected that in many cases
the data coverage requirements will be as for a dedicated FLS trial (see also in Section 7.2) however that
consideration should be part of the measurement campaign design as discussed in Section 6.2.
RP 104: KPIs for wind speed and direction accuracy: pre-deployment check
The applicable KPIs are those described in Section 7.2.
RP 105: Wind speed and direction functionality checks at wind resource assessment site
It is assumed that at the wind resource assessment site there is no nearby high quality reference wind speed
or direction measurement system available. A functionality check using other available sources of data
should be carried out on the wind speed and direction data capture, as would be the case for any other
primary measurement system used in wind resource assessment. The nature of such functionality checks is
an established element of the wind resource assessment discipline and not in the scope of this document.
8.3
SENSITIVITY OF WIND SPEED AND DIRECTION ACCURACY RESULTS
RP 106: Sensitivity of wind speed and direction error: pre-deployment checks
The sensitivity of wind speed and direction accuracy of the FLS during the pre-deployment check, should be
assessed as described for a dedicated FLS trial in Section 7.3.
RP 107: Wind speed and direction and sensitivity to environmental parameters
Wind speed and direction data captured at the wind resource assessment site, whereby the environmental
parameters experienced fall outside those experienced in previous full-scale trials and in the pre-deployment
56
checks, will necessarily be regarded with less confidence. In a manner analogous to the sensitivity studies in
a full-scale trial (see Section 7.3), the captured wind data should be binned by the pre-determined measured
quantities (see Sections 5.5 and 6.5), and separate analyses carried out for all data and only for data falling
in previously experienced ranges. Comparison of these separate analyses is likely to be informative. The
most conservative course of action is to exclude all data outside previously-experienced ranges, however
there may well be strong justification for including some or all of that data – this should be considered on a
case-by-case basis.
8.4
AVAILABILITY
The KPIs defined for a full-scale trial (see Section 7.4) should be used, for both the pre-deployment
verification phase and the wind resource assessment phase.
KPIs for Number of Maintenance Visits, Number of Unscheduled Outages, Uptime of Communication
System defined for a full-scale trial (see Section 7.4) should be used, for both the pre-deployment verification
phase and the wind resource assessment phase.
8.5
ACCEPTANCE CRITERIA
RP 110: Pre-deployment verification acceptance criteria – accuracy
Suitable acceptance thresholds for accuracy are summarised in Table 4. These are applicable to the predeployment verification phase for the FLS. These thresholds should not be interpreted as binary pass/fail
criteria, but should be interpreted by suitably qualified and experienced analysts.
RP 111: Pre-deployment verification and wind resource assessment acceptance criteria - availability
Suitable acceptance thresholds for availability are summarised in Table 5. These are applicable to the predeployment verification phase for the FLS. For the wind resource acceptance phase, these are a useful
guide to expected performance. These thresholds should not be interpreted as binary pass/fail criteria, but
should be interpreted by suitably qualified and experienced analysts.
8.6
ASSESSMENT OF UNCERTAINTY OF FLS MEASUREMENTS
Note 27: Considerations on the FLS measurement uncertainty
A measurement uncertainty assessment should be made for the resulting wind data. This should be carried
out on a case-by-case basis with the following factors taken into account as a minimum:

Supplier evidence of FLS maturity (see Section 3.2), and any other FLS trial data;

Results from pre-deployment verification (see Section 8.2);

The range of environmental conditions experienced (see Section 8.3);

Any observations from operating experience which may be relevant to confidence in the data.
In addition, the OWA roadmap [10] includes some considerations on expected levels of measurement
uncertainty.
57
8.7
LESSONS LEARNT
The opportunity to learn from experience during a FLS deployment is considerable. It is recommended that
there is a formal “lessons learnt” activity involving all stakeholders on completion of the campaign. The scope
of the activity should include all aspects including planning, procurement, deployment, maintenance,
recovery as well as system accuracy and reliability. Where possible and acknowledging commercial
sensitivities, details of lessons learnt should be disseminated to the offshore wind industry in general.
58
9.
RECOMMENDATIONS FOR FURTHER WORK
In the course of developing this recommended practice document the authors are aware that this is a
“stepping-stone” on the way to a normative standard. As is natural in such a case, a number of areas have
been identified where the industry would benefit from further work on developing or codifying recommended
practice. These are summarised as follows:
1. Development of classification issues. Currently there is no scheme for classifying floating lidar
systems, or for classifying sites in terms of characteristics relevant to floating lidar system
deployment.
2. Measurement uncertainty. Guidance on generating an uncertainty budget for the use of a floating
lidar system in wind resource assessment; support for this from floating lidar system trials. Preferably
the guidance would be prescriptive in nature, and would include considerations on the consistency
between units of the same type.
3. Guidance on mooring design and on assessment of mooring design.
4. Safety issues. A site operator will have to consider all aspects of safety as ultimately they will have
responsibility for safety with respect to their own personnel, the environment and other parties e.g.
shipping. Rather than considering on a case-by-case basis, developing recommended practice
would be likely to reduce the burden on the site operator and hence reduce the cost of adopting the
technology.
5. Case Study. Illustration of all of the points in this document, and in future developments of this
document, through a record of how each element was tackled for a real case study, would be very
informative.
6. Metocean Sensors. A more prescriptive specification of the standards of metocean sensors
required, including when provision of such sensors onboard the floating lidar platform is advisable or
not advisable.
7. Standards for trusted reference system. Acceptable uncertainty levels for the trusted reference
system necessary for a floating lidar system trial,
8. Pre-deployment verification. More guidance on when a pre-deployment verification is required.
9. Representativeness / comparisons of wave climates. When a system is trialled in one climate,
but deployed in another, this raises questions. More guidance on how to tackle this challenge could
be developed.
10. Understanding gust and turbulence. What value can be derived from gust and turbulence
measurements from floating lidar systems?
11. Non-wind resource assessment uses. For example, wind turbine power curve estimation.
12. Development of a repository of floating lidar system applications.
All of the above items are considered to be achievable without further early-stage research. Items 1 to 5 are
considered by the authors to be the highest priority items here but are otherwise in no particular order. It is
the authors’ recommendation that these areas, and any others prioritised by industry stakeholders, are
included in a future iteration of this document.
59
10.
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June 2009.
13. MEASNET, Evaluation of Site-Specific Wind Conditions, Version 1, 2009.
14. Smith M., OWA floating Lidar campaign: Babcock trial at Gwynt Y Môr, EWEA Offshore 2015,
Copenhagen, 11 March 2015.
15. IEC 61400-12-1 Ed. 2 CDV / Annex L.4
60
APPENDIX: PLANNING AND PERMITTING
This section makes some general comments which should be useful for owner/operators engaging with the
statutory licensing, planning and/or permitting authorities. Although a few specific notes are made, they are
generic in nature because the engagement required, and the authorities involved, vary significantly between
jurisdictions.
10.1
USING THIS SECTION
this section is useful for aiding their understanding of the FLS permitting context, and planning activity and
timescales accordingly.
10.2
NOTES AND RECOMMENDATIONS RELATED TO PERMITTING
Note 28: Licensing – general.
Experience has shown that, for both suppliers and for owner/operators, the initial expectations of timescales
to obtain the necessary consents can easily be underestimated. Consenting timescales can be the pacing
item for floating lidar deployments, with a 16-week period being seen as realistic based on UK waters, and 8
weeks perhaps typical in German waters. It is not clear how this varies with different types of FLS, e.g.
marine buoys versus spar buoys. Some additional observations are as follows:

For a FLS trial, where it is required to locate the FLS close to a met mast, it can be quicker to deploy
the FLS within the mast operator’s area of responsibility (close to the mast) compared to outside this
area.

Current and prior usage of the proposed mast location can have a strong bearing on the timescale
required for consenting.
RP 113: Engagement with authorities.
It is recommended to become aware of and consult with the relevant authorities as early as possible in the
process, and if possible engage in an active dialogue to reduce the risk of delay.
Note 29: Licensing – vessel classification.
The FLS may not conform neatly with existing vessel classifications used by licensing authorities. The
manner in which the buoy or floating platform is described in the consenting application can complicate the
approval, and making progress on this topic can be expedited by actively seeking individuals with prior
experience and/or an active dialogue with the licensing authorities.
Note 30: Specific learning points from a UK waters deployment in the Irish Sea
The following requirements for making a FLS marine license application (note in UK waters) have been
provided by RWE following an FLS trial (see [8]) carried out in the Irish Sea:

Description of the FLS to be used, including photograph of the device

Schematic diagrams of the FLS and the mooring system

Duration of the project (start/end date)

Location of the FLS - Lat/Long - degree and decimal minutes. (e.g. 3° 30.48'W 53° 28.78'N)
61

Contractor details

Full details of the proposed project, including the method of construction

Justification for its requirement on the project

Area influence of the FLS (i.e. area within which it can drift with the proposed mooring system)

Detailed method of construction, and measures to be taken, to minimise any risk to the marine
environment, prevent undue interference to others, mooring of barges, pontoons, transhipment
vessels, maintain navigational safety, including marking and lighting of works.

Height of the highest point on the buoy above the water surface.

Dimensions of the mooring to cover the seabed, and tonnage.

Details of the power generation and power storage equipment on the buoy.

Frequency of potential servicing and refuelling activities.

Description of the mooring system

Mooring material datasheet - including source of material.

Description of how the FLS will be deployed (timescales and vessel if known). Vessel specification
document (can be provided at a later stage if unknown)

Deployment method statement (pictures of deployment method, if available)

Vessel route plan - description of the method of delivery.

Decommissioning plan

Map 1 - scaled to 1:25,000 of larger, admiralty chart, mean high water spring mark, FLS location,
project area/lease boundary, other constraints (other users of the sea, for example; navigation,
dredging licences etc), environmental sensitive areas (SPA, SAC, SSSI, RAMSAR, NNR, LNR,
Areas of outstanding natural beauty).

Map 2 - schematic drawing on a location plan (1:2,500 to 1:10,000, A4 or A3) showing the full extent
of the project in relation to the surrounding area.

Reporting on benthic environment from the project - technical report produced for the EIA, or preconstruction benthic survey work (consents team should already have this)

Stakeholder discussions
-
Trinity House Lighthouse Service and the Maritime and Coastguard Agency, with regards to
safe navigation lightings and markings.
-
The Crown Estate agreement
-
Public notices of the consent application are required - identify two locations in the vicinity of
the project/or port (e.g. library/museum/arts centre).
62

Recommended Practices for Floating Lidar Systems

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